[PATCH] staging: iio: ade7753: replace mlock with driver private lock

[PATCH] staging: iio: ade7753: replace mlock with driver private lock

[simran singhal]

The IIO subsystem is redefining iio_dev->mlock to be used by
the IIO core only for protecting device operating mode changes.
ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.

In this driver, mlock was being used to protect hardware state
changes.  Replace it with a lock in the devices global data.

Fix some coding style issues related to white space also.

Signed-off-by: simran singhal <singhalsimran0@gmail.com>
---
 drivers/staging/iio/meter/ade7753.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
index dfd8b71..ca99d82 100644
--- a/drivers/staging/iio/meter/ade7753.c
+++ b/drivers/staging/iio/meter/ade7753.c
@@ -81,12 +81,14 @@
  * @tx:         transmit buffer
  * @rx:         receive buffer
  * @buf_lock:       mutex to protect tx and rx
+ * @lock:	protect sensor state
  **/
 struct ade7753_state {
-	    struct spi_device   *us;
-		    struct mutex        buf_lock;
-			    u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
-				    u8          rx[ADE7753_MAX_RX];
+	struct spi_device   *us;
+	struct mutex        buf_lock;
+	struct mutex        lock;	/* protect sensor state */
+	u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
+	u8          rx[ADE7753_MAX_RX];
 };
 
 static int ade7753_spi_write_reg_8(struct device *dev,
@@ -484,7 +486,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
 	if (!val)
 		return -EINVAL;
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&st->lock);
 
 	t = 27900 / val;
 	if (t > 0)
@@ -505,7 +507,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
 	ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
 
 out:
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&st->lock);
 
 	return ret ? ret : len;
 }
-- 
2.7.4

Re: [Outreachy kernel] [PATCH] staging: iio: ade7753: replace mlock with driver private lock

[Alison Schofield]

On Sun, Mar 12, 2017 at 07:02:50PM +0530, simran singhal wrote:
> The IIO subsystem is redefining iio_dev->mlock to be used by
> the IIO core only for protecting device operating mode changes.
> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
> 
> In this driver, mlock was being used to protect hardware state
> changes.  Replace it with a lock in the devices global data.
> 
> Fix some coding style issues related to white space also.
> 
> Signed-off-by: simran singhal <singhalsimran0@gmail.com>

Hi Simran, This looks good to me.  Let's see what the
reviewers say.  I think the white space stuff is ok,
since it was right where you were editing. 
alisons

> ---
>  drivers/staging/iio/meter/ade7753.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
> index dfd8b71..ca99d82 100644
> --- a/drivers/staging/iio/meter/ade7753.c
> +++ b/drivers/staging/iio/meter/ade7753.c
> @@ -81,12 +81,14 @@
>   * @tx:         transmit buffer
>   * @rx:         receive buffer
>   * @buf_lock:       mutex to protect tx and rx
> + * @lock:	protect sensor state
>   **/
>  struct ade7753_state {
> -	    struct spi_device   *us;
> -		    struct mutex        buf_lock;
> -			    u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
> -				    u8          rx[ADE7753_MAX_RX];
> +	struct spi_device   *us;
> +	struct mutex        buf_lock;
> +	struct mutex        lock;	/* protect sensor state */
> +	u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
> +	u8          rx[ADE7753_MAX_RX];
>  };
>  
>  static int ade7753_spi_write_reg_8(struct device *dev,
> @@ -484,7 +486,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>  	if (!val)
>  		return -EINVAL;
>  
> -	mutex_lock(&indio_dev->mlock);
> +	mutex_lock(&st->lock);
>  
>  	t = 27900 / val;
>  	if (t > 0)
> @@ -505,7 +507,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>  	ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
>  
>  out:
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&st->lock);
>  
>  	return ret ? ret : len;
>  }
> -- 
> 2.7.4
> 
> -- 
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> For more options, visit https://groups.google.com/d/optout.

Re: [Outreachy kernel] [PATCH] staging: iio: ade7753: replace mlock with driver private lock

[SIMRAN SINGHAL]

On Mon, Mar 13, 2017 at 12:03 AM, Alison Schofield <amsfield22@gmail.com> wrote:
> On Sun, Mar 12, 2017 at 07:02:50PM +0530, simran singhal wrote:
>> The IIO subsystem is redefining iio_dev->mlock to be used by
>> the IIO core only for protecting device operating mode changes.
>> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
>>
>> In this driver, mlock was being used to protect hardware state
>> changes.  Replace it with a lock in the devices global data.
>>
>> Fix some coding style issues related to white space also.
>>
>> Signed-off-by: simran singhal <singhalsimran0@gmail.com>
>
> Hi Simran, This looks good to me.  Let's see what the
> reviewers say.  I think the white space stuff is ok,
> since it was right where you were editing.
> alisons
>
Alison, so sending this patch here on outreachy mailing list is fine.
Still confuse :P

>> ---
>>  drivers/staging/iio/meter/ade7753.c | 14 ++++++++------
>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
>> index dfd8b71..ca99d82 100644
>> --- a/drivers/staging/iio/meter/ade7753.c
>> +++ b/drivers/staging/iio/meter/ade7753.c
>> @@ -81,12 +81,14 @@
>>   * @tx:         transmit buffer
>>   * @rx:         receive buffer
>>   * @buf_lock:       mutex to protect tx and rx
>> + * @lock:    protect sensor state
>>   **/
>>  struct ade7753_state {
>> -         struct spi_device   *us;
>> -                 struct mutex        buf_lock;
>> -                         u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>> -                                 u8          rx[ADE7753_MAX_RX];
>> +     struct spi_device   *us;
>> +     struct mutex        buf_lock;
>> +     struct mutex        lock;       /* protect sensor state */
>> +     u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>> +     u8          rx[ADE7753_MAX_RX];
>>  };
>>
>>  static int ade7753_spi_write_reg_8(struct device *dev,
>> @@ -484,7 +486,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>       if (!val)
>>               return -EINVAL;
>>
>> -     mutex_lock(&indio_dev->mlock);
>> +     mutex_lock(&st->lock);
>>
>>       t = 27900 / val;
>>       if (t > 0)
>> @@ -505,7 +507,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>       ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
>>
>>  out:
>> -     mutex_unlock(&indio_dev->mlock);
>> +     mutex_unlock(&st->lock);
>>
>>       return ret ? ret : len;
>>  }
>> --
>> 2.7.4
>>
>> --
>> You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
>> To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
>> To post to this group, send email to outreachy-kernel@googlegroups.com.
>> To view this discussion on the web visit https://groups.google.com/d/msgid/outreachy-kernel/20170312133250.GA7772%40singhal-Inspiron-5558.
>> For more options, visit https://groups.google.com/d/optout.

Re: [Outreachy kernel] [PATCH] staging: iio: ade7753: replace mlock with driver private lock

[Alison Schofield]

On Mon, Mar 13, 2017 at 09:28:34AM +0530, SIMRAN SINGHAL wrote:
> On Mon, Mar 13, 2017 at 12:03 AM, Alison Schofield <amsfield22@gmail.com> wrote:
> > On Sun, Mar 12, 2017 at 07:02:50PM +0530, simran singhal wrote:
> >> The IIO subsystem is redefining iio_dev->mlock to be used by
> >> the IIO core only for protecting device operating mode changes.
> >> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
> >>
> >> In this driver, mlock was being used to protect hardware state
> >> changes.  Replace it with a lock in the devices global data.
> >>
> >> Fix some coding style issues related to white space also.
> >>
> >> Signed-off-by: simran singhal <singhalsimran0@gmail.com>
> >
> > Hi Simran, This looks good to me.  Let's see what the
> > reviewers say.  I think the white space stuff is ok,
> > since it was right where you were editing.
> > alisons
> >
> Alison, so sending this patch here on outreachy mailing list is fine.
> Still confuse :P

You are OK.  You sent it to everyone suggested in the Task Description.

This patch was sent before I posted the Task Description.  I'm assuming
that since then you've found the posted Task:
https://kernelnewbies.org/IIO_tasks 
Find Coding Task 2 --> "PATCHES need to be sent to all of:"

> 
> >> ---
> >>  drivers/staging/iio/meter/ade7753.c | 14 ++++++++------
> >>  1 file changed, 8 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
> >> index dfd8b71..ca99d82 100644
> >> --- a/drivers/staging/iio/meter/ade7753.c
> >> +++ b/drivers/staging/iio/meter/ade7753.c
> >> @@ -81,12 +81,14 @@
> >>   * @tx:         transmit buffer
> >>   * @rx:         receive buffer
> >>   * @buf_lock:       mutex to protect tx and rx
> >> + * @lock:    protect sensor state
> >>   **/
> >>  struct ade7753_state {
> >> -         struct spi_device   *us;
> >> -                 struct mutex        buf_lock;
> >> -                         u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
> >> -                                 u8          rx[ADE7753_MAX_RX];
> >> +     struct spi_device   *us;
> >> +     struct mutex        buf_lock;
> >> +     struct mutex        lock;       /* protect sensor state */
> >> +     u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
> >> +     u8          rx[ADE7753_MAX_RX];
> >>  };
> >>
> >>  static int ade7753_spi_write_reg_8(struct device *dev,
> >> @@ -484,7 +486,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
> >>       if (!val)
> >>               return -EINVAL;
> >>
> >> -     mutex_lock(&indio_dev->mlock);
> >> +     mutex_lock(&st->lock);
> >>
> >>       t = 27900 / val;
> >>       if (t > 0)
> >> @@ -505,7 +507,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
> >>       ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
> >>
> >>  out:
> >> -     mutex_unlock(&indio_dev->mlock);
> >> +     mutex_unlock(&st->lock);
> >>
> >>       return ret ? ret : len;
> >>  }
> >> --
> >> 2.7.4
> >>
> >> --
> >> You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
> >> To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
> >> To post to this group, send email to outreachy-kernel@googlegroups.com.
> >> To view this discussion on the web visit https://groups.google.com/d/msgid/outreachy-kernel/20170312133250.GA7772%40singhal-Inspiron-5558.
> >> For more options, visit https://groups.google.com/d/optout.

Re: [PATCH] staging: iio: ade7753: replace mlock with driver private lock

[Lars-Peter Clausen]

On 03/12/2017 02:32 PM, simran singhal wrote:
> The IIO subsystem is redefining iio_dev->mlock to be used by
> the IIO core only for protecting device operating mode changes.
> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
> 
> In this driver, mlock was being used to protect hardware state
> changes.  Replace it with a lock in the devices global data.
> 
> Fix some coding style issues related to white space also.
> 
> Signed-off-by: simran singhal <singhalsimran0@gmail.com>
> ---
>  drivers/staging/iio/meter/ade7753.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
> index dfd8b71..ca99d82 100644
> --- a/drivers/staging/iio/meter/ade7753.c
> +++ b/drivers/staging/iio/meter/ade7753.c
> @@ -81,12 +81,14 @@
>   * @tx:         transmit buffer
>   * @rx:         receive buffer
>   * @buf_lock:       mutex to protect tx and rx
> + * @lock:	protect sensor state

It might make sense to reuse the existing lock which currently protects the
read/write functions. You can do this by introducing a variant of
ade7753_spi_{read,write}_reg_16() that does not take a lock and use these to
implement the read-modify-write cycle in a protected section.

Looking through the driver there seem to be other places as well that do
read-modify-write that should be protected by a lock, but currently are not.
This might be a good task.

>   **/
>  struct ade7753_state {
> -	    struct spi_device   *us;
> -		    struct mutex        buf_lock;
> -			    u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
> -				    u8          rx[ADE7753_MAX_RX];
> +	struct spi_device   *us;
> +	struct mutex        buf_lock;
> +	struct mutex        lock;	/* protect sensor state */
> +	u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
> +	u8          rx[ADE7753_MAX_RX];
>  };
>  
>  static int ade7753_spi_write_reg_8(struct device *dev,
> @@ -484,7 +486,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>  	if (!val)
>  		return -EINVAL;
>  
> -	mutex_lock(&indio_dev->mlock);
> +	mutex_lock(&st->lock);
>  
>  	t = 27900 / val;
>  	if (t > 0)
> @@ -505,7 +507,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>  	ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
>  
>  out:
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&st->lock);
>  
>  	return ret ? ret : len;
>  }
> 

Re: [PATCH] staging: iio: ade7753: replace mlock with driver private lock

[SIMRAN SINGHAL]

On Mon, Mar 13, 2017 at 5:30 PM, Lars-Peter Clausen <lars@metafoo.de> wrote:
> On 03/12/2017 02:32 PM, simran singhal wrote:
>> The IIO subsystem is redefining iio_dev->mlock to be used by
>> the IIO core only for protecting device operating mode changes.
>> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
>>
>> In this driver, mlock was being used to protect hardware state
>> changes.  Replace it with a lock in the devices global data.
>>
>> Fix some coding style issues related to white space also.
>>
>> Signed-off-by: simran singhal <singhalsimran0@gmail.com>
>> ---
>>  drivers/staging/iio/meter/ade7753.c | 14 ++++++++------
>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
>> index dfd8b71..ca99d82 100644
>> --- a/drivers/staging/iio/meter/ade7753.c
>> +++ b/drivers/staging/iio/meter/ade7753.c
>> @@ -81,12 +81,14 @@
>>   * @tx:         transmit buffer
>>   * @rx:         receive buffer
>>   * @buf_lock:       mutex to protect tx and rx
>> + * @lock:    protect sensor state
>
> It might make sense to reuse the existing lock which currently protects the
> read/write functions. You can do this by introducing a variant of
> ade7753_spi_{read,write}_reg_16() that does not take a lock and use these to
> implement the read-modify-write cycle in a protected section.
>
> Looking through the driver there seem to be other places as well that do
> read-modify-write that should be protected by a lock, but currently are not.
> This might be a good task.
>

Are you trying to say that their is no need of introducing "lock",
I can using "buf_lock" only.

Thanks!

>>   **/
>>  struct ade7753_state {
>> -         struct spi_device   *us;
>> -                 struct mutex        buf_lock;
>> -                         u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>> -                                 u8          rx[ADE7753_MAX_RX];
>> +     struct spi_device   *us;
>> +     struct mutex        buf_lock;
>> +     struct mutex        lock;       /* protect sensor state */
>> +     u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>> +     u8          rx[ADE7753_MAX_RX];
>>  };
>>
>>  static int ade7753_spi_write_reg_8(struct device *dev,
>> @@ -484,7 +486,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>       if (!val)
>>               return -EINVAL;
>>
>> -     mutex_lock(&indio_dev->mlock);
>> +     mutex_lock(&st->lock);
>>
>>       t = 27900 / val;
>>       if (t > 0)
>> @@ -505,7 +507,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>       ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
>>
>>  out:
>> -     mutex_unlock(&indio_dev->mlock);
>> +     mutex_unlock(&st->lock);
>>
>>       return ret ? ret : len;
>>  }
>>
>

Re: [PATCH] staging: iio: ade7753: replace mlock with driver private lock

[Lars-Peter Clausen]

On 03/13/2017 01:33 PM, SIMRAN SINGHAL wrote:
> On Mon, Mar 13, 2017 at 5:30 PM, Lars-Peter Clausen <lars@metafoo.de> wrote:
>> On 03/12/2017 02:32 PM, simran singhal wrote:
>>> The IIO subsystem is redefining iio_dev->mlock to be used by
>>> the IIO core only for protecting device operating mode changes.
>>> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
>>>
>>> In this driver, mlock was being used to protect hardware state
>>> changes.  Replace it with a lock in the devices global data.
>>>
>>> Fix some coding style issues related to white space also.
>>>
>>> Signed-off-by: simran singhal <singhalsimran0@gmail.com>
>>> ---
>>>  drivers/staging/iio/meter/ade7753.c | 14 ++++++++------
>>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
>>> index dfd8b71..ca99d82 100644
>>> --- a/drivers/staging/iio/meter/ade7753.c
>>> +++ b/drivers/staging/iio/meter/ade7753.c
>>> @@ -81,12 +81,14 @@
>>>   * @tx:         transmit buffer
>>>   * @rx:         receive buffer
>>>   * @buf_lock:       mutex to protect tx and rx
>>> + * @lock:    protect sensor state
>>
>> It might make sense to reuse the existing lock which currently protects the
>> read/write functions. You can do this by introducing a variant of
>> ade7753_spi_{read,write}_reg_16() that does not take a lock and use these to
>> implement the read-modify-write cycle in a protected section.
>>
>> Looking through the driver there seem to be other places as well that do
>> read-modify-write that should be protected by a lock, but currently are not.
>> This might be a good task.
>>
> 
> Are you trying to say that their is no need of introducing "lock",
> I can using "buf_lock" only.

Yes, there should be no need for two locks. But you need to slightly
refactor the code to avoid taking the same lock nested.

> 
> Thanks!
> 
>>>   **/
>>>  struct ade7753_state {
>>> -         struct spi_device   *us;
>>> -                 struct mutex        buf_lock;
>>> -                         u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>>> -                                 u8          rx[ADE7753_MAX_RX];
>>> +     struct spi_device   *us;
>>> +     struct mutex        buf_lock;
>>> +     struct mutex        lock;       /* protect sensor state */
>>> +     u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>>> +     u8          rx[ADE7753_MAX_RX];
>>>  };
>>>
>>>  static int ade7753_spi_write_reg_8(struct device *dev,
>>> @@ -484,7 +486,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>>       if (!val)
>>>               return -EINVAL;
>>>
>>> -     mutex_lock(&indio_dev->mlock);
>>> +     mutex_lock(&st->lock);
>>>
>>>       t = 27900 / val;
>>>       if (t > 0)
>>> @@ -505,7 +507,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>>       ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
>>>
>>>  out:
>>> -     mutex_unlock(&indio_dev->mlock);
>>> +     mutex_unlock(&st->lock);
>>>
>>>       return ret ? ret : len;
>>>  }
>>>
>>

Re: [Outreachy kernel] Re: [PATCH] staging: iio: ade7753: replace mlock with driver private lock

[Gargi Sharma]

On Mon, Mar 13, 2017 at 5:30 PM, Lars-Peter Clausen <lars@metafoo.de> wrote:
>
> On 03/12/2017 02:32 PM, simran singhal wrote:
> > The IIO subsystem is redefining iio_dev->mlock to be used by
> > the IIO core only for protecting device operating mode changes.
> > ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
> >
> > In this driver, mlock was being used to protect hardware state
> > changes.  Replace it with a lock in the devices global data.
> >
> > Fix some coding style issues related to white space also.
> >
> > Signed-off-by: simran singhal <singhalsimran0@gmail.com>
> > ---
> >  drivers/staging/iio/meter/ade7753.c | 14 ++++++++------
> >  1 file changed, 8 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
> > index dfd8b71..ca99d82 100644
> > --- a/drivers/staging/iio/meter/ade7753.c
> > +++ b/drivers/staging/iio/meter/ade7753.c
> > @@ -81,12 +81,14 @@
> >   * @tx:         transmit buffer
> >   * @rx:         receive buffer
> >   * @buf_lock:       mutex to protect tx and rx
> > + * @lock:    protect sensor state
>
> It might make sense to reuse the existing lock which currently protects the
> read/write functions. You can do this by introducing a variant of
> ade7753_spi_{read,write}_reg_16() that does not take a lock and use these to
> implement the read-modify-write cycle in a protected section.

There are other read/write functions for example,
ade7753_spi_{read/write}_reg_8 that use the mutex as well. Should a
variant of these functions be introduced as well? Also, how does one
go about implementing RMW inside a protected section.


>
> Looking through the driver there seem to be other places as well that do
> read-modify-write that should be protected by a lock, but currently are not.
> This might be a good task.

Am I right in understanding that we want to introduce mutex lock for
writes in other drivers as well?

Thanks,
Gargi
>
> >   **/
> >  struct ade7753_state {
> > -         struct spi_device   *us;
> > -                 struct mutex        buf_lock;
> > -                         u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
> > -                                 u8          rx[ADE7753_MAX_RX];
> > +     struct spi_device   *us;
> > +     struct mutex        buf_lock;
> > +     struct mutex        lock;       /* protect sensor state */
> > +     u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
> > +     u8          rx[ADE7753_MAX_RX];
> >  };
> >
> >  static int ade7753_spi_write_reg_8(struct device *dev,
> > @@ -484,7 +486,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
> >       if (!val)
> >               return -EINVAL;
> >
> > -     mutex_lock(&indio_dev->mlock);
> > +     mutex_lock(&st->lock);
> >
> >       t = 27900 / val;
> >       if (t > 0)
> > @@ -505,7 +507,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
> >       ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
> >
> >  out:
> > -     mutex_unlock(&indio_dev->mlock);
> > +     mutex_unlock(&st->lock);
> >
> >       return ret ? ret : len;
> >  }
> >
>
> --

Re: [Outreachy kernel] Re: [PATCH] staging: iio: ade7753: replace mlock with driver private lock

[Jonathan Cameron]

On 17/03/17 09:32, Gargi Sharma wrote:
> On Mon, Mar 13, 2017 at 5:30 PM, Lars-Peter Clausen <lars@metafoo.de> wrote:
>>
>> On 03/12/2017 02:32 PM, simran singhal wrote:
>>> The IIO subsystem is redefining iio_dev->mlock to be used by
>>> the IIO core only for protecting device operating mode changes.
>>> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
>>>
>>> In this driver, mlock was being used to protect hardware state
>>> changes.  Replace it with a lock in the devices global data.
>>>
>>> Fix some coding style issues related to white space also.
>>>
>>> Signed-off-by: simran singhal <singhalsimran0@gmail.com>
>>> ---
>>>  drivers/staging/iio/meter/ade7753.c | 14 ++++++++------
>>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
>>> index dfd8b71..ca99d82 100644
>>> --- a/drivers/staging/iio/meter/ade7753.c
>>> +++ b/drivers/staging/iio/meter/ade7753.c
>>> @@ -81,12 +81,14 @@
>>>   * @tx:         transmit buffer
>>>   * @rx:         receive buffer
>>>   * @buf_lock:       mutex to protect tx and rx
>>> + * @lock:    protect sensor state
>>
>> It might make sense to reuse the existing lock which currently protects the
>> read/write functions. You can do this by introducing a variant of
>> ade7753_spi_{read,write}_reg_16() that does not take a lock and use these to
>> implement the read-modify-write cycle in a protected section.
> 
> There are other read/write functions for example,
> ade7753_spi_{read/write}_reg_8 that use the mutex as well. Should a
> variant of these functions be introduced as well? Also, how does one
> go about implementing RMW inside a protected section.
Hmm. Simran has also been progressing with patches for this.

You raise a good question. There are other read/modify/write sequences in
the driver.  They don't have the same issue with potentially deadlocking
against the buf lock as they are all using the spi subsystems provisions
for small write/read cycles where buffer protection is handled internally.

So let us address the cases in turn:

static int ade7753_reset(struct device *dev)
{
	u16 val;
	int ret;

	ret = ade7753_spi_read_reg_16(dev, ADE7753_MODE, &val);
	if (ret)
		return ret;

	val |= BIT(6); /* Software Chip Reset */

	return ade7753_spi_write_reg_16(dev, ADE7753_MODE, val);
}
This is only called in the device initialization.  At that point
we should be fine in assuming no parallel calls.  Crucial point
is it is before the call to iio_device_register which exposes
the userspace interfaces.

static int ade7753_set_irq(struct device *dev, bool enable)
{
	int ret;
	u8 irqen;

	ret = ade7753_spi_read_reg_8(dev, ADE7753_IRQEN, &irqen);
	if (ret)
		goto error_ret;

	if (enable)
		irqen |= BIT(3); /* Enables an interrupt when a data is
				  * present in the waveform register
				  */
	else
		irqen &= ~BIT(3);

	ret = ade7753_spi_write_reg_8(dev, ADE7753_IRQEN, irqen);

error_ret:
	return ret;
}

This one is actually safe because it is the only function that
modifies that particular register.

/* Power down the device */
static int ade7753_stop_device(struct device *dev)
{
	u16 val;
	int ret;

	ret = ade7753_spi_read_reg_16(dev, ADE7753_MODE, &val);
	if (ret)
		return ret;

	val |= BIT(4);  /* AD converters can be turned off */

	return ade7753_spi_write_reg_16(dev, ADE7753_MODE, val);
}

Only called in remove (after userspace interfaces have been
removed by the iio_device_unregister call so also should not
be running concurrently with much else.

So I think all the other cases are safe.  Perhaps it would have
been better to have had a lock around them, purely to make
the code more resilient against future changes though.  
Probably a job to do as part of a larger scale pile of work
on that driver rather than as a one off patch.

Jonathan







> 
> 
>>
>> Looking through the driver there seem to be other places as well that do
>> read-modify-write that should be protected by a lock, but currently are not.
>> This might be a good task.
> 
> Am I right in understanding that we want to introduce mutex lock for
> writes in other drivers as well?
> 
> Thanks,
> Gargi
>>
>>>   **/
>>>  struct ade7753_state {
>>> -         struct spi_device   *us;
>>> -                 struct mutex        buf_lock;
>>> -                         u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>>> -                                 u8          rx[ADE7753_MAX_RX];
>>> +     struct spi_device   *us;
>>> +     struct mutex        buf_lock;
>>> +     struct mutex        lock;       /* protect sensor state */
>>> +     u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>>> +     u8          rx[ADE7753_MAX_RX];
>>>  };
>>>
>>>  static int ade7753_spi_write_reg_8(struct device *dev,
>>> @@ -484,7 +486,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>>       if (!val)
>>>               return -EINVAL;
>>>
>>> -     mutex_lock(&indio_dev->mlock);
>>> +     mutex_lock(&st->lock);
>>>
>>>       t = 27900 / val;
>>>       if (t > 0)
>>> @@ -505,7 +507,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>>       ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
>>>
>>>  out:
>>> -     mutex_unlock(&indio_dev->mlock);
>>> +     mutex_unlock(&st->lock);
>>>
>>>       return ret ? ret : len;
>>>  }
>>>
>>
>> --
> --
> To unsubscribe from this list: send the line "unsubscribe linux-iio" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: [Outreachy kernel] Re: [PATCH] staging: iio: ade7753: replace mlock with driver private lock

[Gargi Sharma]

On Sun, Mar 19, 2017 at 4:01 PM, Jonathan Cameron <jic23@kernel.org> wrote:
> On 17/03/17 09:32, Gargi Sharma wrote:
>> On Mon, Mar 13, 2017 at 5:30 PM, Lars-Peter Clausen <lars@metafoo.de> wrote:
>>>
>>> On 03/12/2017 02:32 PM, simran singhal wrote:
>>>> The IIO subsystem is redefining iio_dev->mlock to be used by
>>>> the IIO core only for protecting device operating mode changes.
>>>> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
>>>>
>>>> In this driver, mlock was being used to protect hardware state
>>>> changes.  Replace it with a lock in the devices global data.
>>>>
>>>> Fix some coding style issues related to white space also.
>>>>
>>>> Signed-off-by: simran singhal <singhalsimran0@gmail.com>
>>>> ---
>>>>  drivers/staging/iio/meter/ade7753.c | 14 ++++++++------
>>>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
>>>> index dfd8b71..ca99d82 100644
>>>> --- a/drivers/staging/iio/meter/ade7753.c
>>>> +++ b/drivers/staging/iio/meter/ade7753.c
>>>> @@ -81,12 +81,14 @@
>>>>   * @tx:         transmit buffer
>>>>   * @rx:         receive buffer
>>>>   * @buf_lock:       mutex to protect tx and rx
>>>> + * @lock:    protect sensor state
>>>
>>> It might make sense to reuse the existing lock which currently protects the
>>> read/write functions. You can do this by introducing a variant of
>>> ade7753_spi_{read,write}_reg_16() that does not take a lock and use these to
>>> implement the read-modify-write cycle in a protected section.
>>
>> There are other read/write functions for example,
>> ade7753_spi_{read/write}_reg_8 that use the mutex as well. Should a
>> variant of these functions be introduced as well? Also, how does one
>> go about implementing RMW inside a protected section.
> Hmm. Simran has also been progressing with patches for this.
>
I was trying to work through a patch for ade7754. So ran into the same
problem :)

> You raise a good question. There are other read/modify/write sequences in
> the driver.  They don't have the same issue with potentially deadlocking
> against the buf lock as they are all using the spi subsystems provisions
> for small write/read cycles where buffer protection is handled internally.
>
> So let us address the cases in turn:
>
> static int ade7753_reset(struct device *dev)
> {
>         u16 val;
>         int ret;
>
>         ret = ade7753_spi_read_reg_16(dev, ADE7753_MODE, &val);
>         if (ret)
>                 return ret;
>
>         val |= BIT(6); /* Software Chip Reset */
>
>         return ade7753_spi_write_reg_16(dev, ADE7753_MODE, val);
> }
> This is only called in the device initialization.  At that point
> we should be fine in assuming no parallel calls.  Crucial point
> is it is before the call to iio_device_register which exposes
> the userspace interfaces.
>
> static int ade7753_set_irq(struct device *dev, bool enable)
> {
>         int ret;
>         u8 irqen;
>
>         ret = ade7753_spi_read_reg_8(dev, ADE7753_IRQEN, &irqen);
>         if (ret)
>                 goto error_ret;
>
>         if (enable)
>                 irqen |= BIT(3); /* Enables an interrupt when a data is
>                                   * present in the waveform register
>                                   */
>         else
>                 irqen &= ~BIT(3);
>
>         ret = ade7753_spi_write_reg_8(dev, ADE7753_IRQEN, irqen);
>
> error_ret:
>         return ret;
> }
>
> This one is actually safe because it is the only function that
> modifies that particular register.
>
> /* Power down the device */
> static int ade7753_stop_device(struct device *dev)
> {
>         u16 val;
>         int ret;
>
>         ret = ade7753_spi_read_reg_16(dev, ADE7753_MODE, &val);
>         if (ret)
>                 return ret;
>
>         val |= BIT(4);  /* AD converters can be turned off */
>
>         return ade7753_spi_write_reg_16(dev, ADE7753_MODE, val);
> }
>
> Only called in remove (after userspace interfaces have been
> removed by the iio_device_unregister call so also should not
> be running concurrently with much else.
>

The only nested lock here is ade7754_spi_write_reg_16, so as long as
that is refactored, it'll be fine.

> So I think all the other cases are safe.  Perhaps it would have
> been better to have had a lock around them, purely to make
> the code more resilient against future changes though.
> Probably a job to do as part of a larger scale pile of work
> on that driver rather than as a one off patch.

Another question that I have is why are we writing inside a read
function(ade7754_spi_read_reg_24)?

static int ade7754_spi_read_reg_24(struct device *dev,
                                   u8 reg_address, u32 *val)
{
        struct iio_dev *indio_dev = dev_to_iio_dev(dev);
        struct ade7754_state *st = iio_priv(indio_dev);
        int ret;
        struct spi_transfer xfers[] = {
                {
                        .tx_buf = st->tx,
                        .rx_buf = st->rx,
                        .bits_per_word = 8,
                        .len = 4,
                },
        };

        mutex_lock(&st->buf_lock);
        st->tx[0] = ADE7754_READ_REG(reg_address);
        st->tx[1] = 0;
        st->tx[2] = 0;
        st->tx[3] = 0;

        ret = spi_sync_transfer(st->us, xfers, ARRAY_SIZE(xfers));
        if (ret) {
                dev_err(&st->us->dev, "problem when reading 24 bit
register 0x%02X",
                        reg_address);
                goto error_ret;
        }
        *val = (st->rx[1] << 16) | (st->rx[2] << 8) | st->rx[3];

error_ret:
        mutex_unlock(&st->buf_lock);
        return ret;
}

Thanks!
Gargi

>
> Jonathan
>
>
>
>
>
>
>
>>
>>
>>>
>>> Looking through the driver there seem to be other places as well that do
>>> read-modify-write that should be protected by a lock, but currently are not.
>>> This might be a good task.
>>
>> Am I right in understanding that we want to introduce mutex lock for
>> writes in other drivers as well?
>>
>> Thanks,
>> Gargi
>>>
>>>>   **/
>>>>  struct ade7753_state {
>>>> -         struct spi_device   *us;
>>>> -                 struct mutex        buf_lock;
>>>> -                         u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>>>> -                                 u8          rx[ADE7753_MAX_RX];
>>>> +     struct spi_device   *us;
>>>> +     struct mutex        buf_lock;
>>>> +     struct mutex        lock;       /* protect sensor state */
>>>> +     u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>>>> +     u8          rx[ADE7753_MAX_RX];
>>>>  };
>>>>
>>>>  static int ade7753_spi_write_reg_8(struct device *dev,
>>>> @@ -484,7 +486,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>>>       if (!val)
>>>>               return -EINVAL;
>>>>
>>>> -     mutex_lock(&indio_dev->mlock);
>>>> +     mutex_lock(&st->lock);
>>>>
>>>>       t = 27900 / val;
>>>>       if (t > 0)
>>>> @@ -505,7 +507,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>>>       ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
>>>>
>>>>  out:
>>>> -     mutex_unlock(&indio_dev->mlock);
>>>> +     mutex_unlock(&st->lock);
>>>>
>>>>       return ret ? ret : len;
>>>>  }
>>>>
>>>
>>> --
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-iio" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>

Re: [Outreachy kernel] Re: [PATCH] staging: iio: ade7753: replace mlock with driver private lock

[Jonathan Cameron]

On 19/03/17 13:16, Gargi Sharma wrote:
> On Sun, Mar 19, 2017 at 4:01 PM, Jonathan Cameron <jic23@kernel.org> wrote:
>> On 17/03/17 09:32, Gargi Sharma wrote:
>>> On Mon, Mar 13, 2017 at 5:30 PM, Lars-Peter Clausen <lars@metafoo.de> wrote:
>>>>
>>>> On 03/12/2017 02:32 PM, simran singhal wrote:
>>>>> The IIO subsystem is redefining iio_dev->mlock to be used by
>>>>> the IIO core only for protecting device operating mode changes.
>>>>> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
>>>>>
>>>>> In this driver, mlock was being used to protect hardware state
>>>>> changes.  Replace it with a lock in the devices global data.
>>>>>
>>>>> Fix some coding style issues related to white space also.
>>>>>
>>>>> Signed-off-by: simran singhal <singhalsimran0@gmail.com>
>>>>> ---
>>>>>  drivers/staging/iio/meter/ade7753.c | 14 ++++++++------
>>>>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
>>>>> index dfd8b71..ca99d82 100644
>>>>> --- a/drivers/staging/iio/meter/ade7753.c
>>>>> +++ b/drivers/staging/iio/meter/ade7753.c
>>>>> @@ -81,12 +81,14 @@
>>>>>   * @tx:         transmit buffer
>>>>>   * @rx:         receive buffer
>>>>>   * @buf_lock:       mutex to protect tx and rx
>>>>> + * @lock:    protect sensor state
>>>>
>>>> It might make sense to reuse the existing lock which currently protects the
>>>> read/write functions. You can do this by introducing a variant of
>>>> ade7753_spi_{read,write}_reg_16() that does not take a lock and use these to
>>>> implement the read-modify-write cycle in a protected section.
>>>
>>> There are other read/write functions for example,
>>> ade7753_spi_{read/write}_reg_8 that use the mutex as well. Should a
>>> variant of these functions be introduced as well? Also, how does one
>>> go about implementing RMW inside a protected section.
>> Hmm. Simran has also been progressing with patches for this.
>>
> I was trying to work through a patch for ade7754. So ran into the same
> problem :)
> 
>> You raise a good question. There are other read/modify/write sequences in
>> the driver.  They don't have the same issue with potentially deadlocking
>> against the buf lock as they are all using the spi subsystems provisions
>> for small write/read cycles where buffer protection is handled internally.
>>
>> So let us address the cases in turn:
>>
>> static int ade7753_reset(struct device *dev)
>> {
>>         u16 val;
>>         int ret;
>>
>>         ret = ade7753_spi_read_reg_16(dev, ADE7753_MODE, &val);
>>         if (ret)
>>                 return ret;
>>
>>         val |= BIT(6); /* Software Chip Reset */
>>
>>         return ade7753_spi_write_reg_16(dev, ADE7753_MODE, val);
>> }
>> This is only called in the device initialization.  At that point
>> we should be fine in assuming no parallel calls.  Crucial point
>> is it is before the call to iio_device_register which exposes
>> the userspace interfaces.
>>
>> static int ade7753_set_irq(struct device *dev, bool enable)
>> {
>>         int ret;
>>         u8 irqen;
>>
>>         ret = ade7753_spi_read_reg_8(dev, ADE7753_IRQEN, &irqen);
>>         if (ret)
>>                 goto error_ret;
>>
>>         if (enable)
>>                 irqen |= BIT(3); /* Enables an interrupt when a data is
>>                                   * present in the waveform register
>>                                   */
>>         else
>>                 irqen &= ~BIT(3);
>>
>>         ret = ade7753_spi_write_reg_8(dev, ADE7753_IRQEN, irqen);
>>
>> error_ret:
>>         return ret;
>> }
>>
>> This one is actually safe because it is the only function that
>> modifies that particular register.
>>
>> /* Power down the device */
>> static int ade7753_stop_device(struct device *dev)
>> {
>>         u16 val;
>>         int ret;
>>
>>         ret = ade7753_spi_read_reg_16(dev, ADE7753_MODE, &val);
>>         if (ret)
>>                 return ret;
>>
>>         val |= BIT(4);  /* AD converters can be turned off */
>>
>>         return ade7753_spi_write_reg_16(dev, ADE7753_MODE, val);
>> }
>>
>> Only called in remove (after userspace interfaces have been
>> removed by the iio_device_unregister call so also should not
>> be running concurrently with much else.
>>
> 
> The only nested lock here is ade7754_spi_write_reg_16, so as long as
> that is refactored, it'll be fine.
> 
>> So I think all the other cases are safe.  Perhaps it would have
>> been better to have had a lock around them, purely to make
>> the code more resilient against future changes though.
>> Probably a job to do as part of a larger scale pile of work
>> on that driver rather than as a one off patch.
> 
> Another question that I have is why are we writing inside a read
> function(ade7754_spi_read_reg_24)?
>
It's a register read (sort of) hence the reg in the name.
It's telling it which register to read by first writing that.
 
> static int ade7754_spi_read_reg_24(struct device *dev,
>                                    u8 reg_address, u32 *val)
> {
>         struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>         struct ade7754_state *st = iio_priv(indio_dev);
>         int ret;
>         struct spi_transfer xfers[] = {
>                 {
>                         .tx_buf = st->tx,
>                         .rx_buf = st->rx,
>                         .bits_per_word = 8,
>                         .len = 4,
>                 },
>         };
> 
>         mutex_lock(&st->buf_lock);
>         st->tx[0] = ADE7754_READ_REG(reg_address);
>         st->tx[1] = 0;
>         st->tx[2] = 0;
>         st->tx[3] = 0;
> 
>         ret = spi_sync_transfer(st->us, xfers, ARRAY_SIZE(xfers));
>         if (ret) {
>                 dev_err(&st->us->dev, "problem when reading 24 bit
> register 0x%02X",
>                         reg_address);
>                 goto error_ret;
>         }
>         *val = (st->rx[1] << 16) | (st->rx[2] << 8) | st->rx[3];
> 
> error_ret:
>         mutex_unlock(&st->buf_lock);
>         return ret;
> }
> 
> Thanks!
> Gargi
> 
>>
>> Jonathan
>>
>>
>>
>>
>>
>>
>>
>>>
>>>
>>>>
>>>> Looking through the driver there seem to be other places as well that do
>>>> read-modify-write that should be protected by a lock, but currently are not.
>>>> This might be a good task.
>>>
>>> Am I right in understanding that we want to introduce mutex lock for
>>> writes in other drivers as well?
>>>
>>> Thanks,
>>> Gargi
>>>>
>>>>>   **/
>>>>>  struct ade7753_state {
>>>>> -         struct spi_device   *us;
>>>>> -                 struct mutex        buf_lock;
>>>>> -                         u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>>>>> -                                 u8          rx[ADE7753_MAX_RX];
>>>>> +     struct spi_device   *us;
>>>>> +     struct mutex        buf_lock;
>>>>> +     struct mutex        lock;       /* protect sensor state */
>>>>> +     u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>>>>> +     u8          rx[ADE7753_MAX_RX];
>>>>>  };
>>>>>
>>>>>  static int ade7753_spi_write_reg_8(struct device *dev,
>>>>> @@ -484,7 +486,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>>>>       if (!val)
>>>>>               return -EINVAL;
>>>>>
>>>>> -     mutex_lock(&indio_dev->mlock);
>>>>> +     mutex_lock(&st->lock);
>>>>>
>>>>>       t = 27900 / val;
>>>>>       if (t > 0)
>>>>> @@ -505,7 +507,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>>>>       ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
>>>>>
>>>>>  out:
>>>>> -     mutex_unlock(&indio_dev->mlock);
>>>>> +     mutex_unlock(&st->lock);
>>>>>
>>>>>       return ret ? ret : len;
>>>>>  }
>>>>>
>>>>
>>>> --
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-iio" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>>

Re: [Outreachy kernel] Re: [PATCH] staging: iio: ade7753: replace mlock with driver private lock

[Gargi Sharma]

On Mon, Mar 13, 2017 at 5:30 PM, Lars-Peter Clausen <lars@metafoo.de> wrote:
> On 03/12/2017 02:32 PM, simran singhal wrote:
>> The IIO subsystem is redefining iio_dev->mlock to be used by
>> the IIO core only for protecting device operating mode changes.
>> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
>>
>> In this driver, mlock was being used to protect hardware state
>> changes.  Replace it with a lock in the devices global data.
>>
>> Fix some coding style issues related to white space also.
>>
>> Signed-off-by: simran singhal <singhalsimran0@gmail.com>
>> ---
>>  drivers/staging/iio/meter/ade7753.c | 14 ++++++++------
>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
>> index dfd8b71..ca99d82 100644
>> --- a/drivers/staging/iio/meter/ade7753.c
>> +++ b/drivers/staging/iio/meter/ade7753.c
>> @@ -81,12 +81,14 @@
>>   * @tx:         transmit buffer
>>   * @rx:         receive buffer
>>   * @buf_lock:       mutex to protect tx and rx
>> + * @lock:    protect sensor state
>
> It might make sense to reuse the existing lock which currently protects the
> read/write functions. You can do this by introducing a variant of
> ade7753_spi_{read,write}_reg_16() that does not take a lock and use these to
> implement the read-modify-write cycle in a protected section.
>

The only instance I was able to find was drivers/iio/adc/vf610_adc.c
where read modify write cycles are present on the register
VF610_REG_ADC_CFG. I believe writel() & readl() is used for this
purpose.

In this case, we want to write to data to a device on the SPI bus. Can
we use writel() for this purpose?

> Looking through the driver there seem to be other places as well that do
> read-modify-write that should be protected by a lock, but currently are not.
> This might be a good task.
>
>>   **/
>>  struct ade7753_state {
>> -         struct spi_device   *us;
>> -                 struct mutex        buf_lock;
>> -                         u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>> -                                 u8          rx[ADE7753_MAX_RX];
>> +     struct spi_device   *us;
>> +     struct mutex        buf_lock;
>> +     struct mutex        lock;       /* protect sensor state */
>> +     u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>> +     u8          rx[ADE7753_MAX_RX];
>>  };
>>
>>  static int ade7753_spi_write_reg_8(struct device *dev,
>> @@ -484,7 +486,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>       if (!val)
>>               return -EINVAL;
>>
>> -     mutex_lock(&indio_dev->mlock);
>> +     mutex_lock(&st->lock);
>>
>>       t = 27900 / val;
>>       if (t > 0)
>> @@ -505,7 +507,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>       ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
>>
>>  out:
>> -     mutex_unlock(&indio_dev->mlock);
>> +     mutex_unlock(&st->lock);
>>
>>       return ret ? ret : len;
>>  }
>>
>
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