[PATCH] drm/tinydrm: mipi-dbi: Fix unbalanced DMA access

[PATCH] drm/tinydrm: mipi-dbi: Fix unbalanced DMA access

[David Lechner]

If we return here and import_attach is true, then dma_buf_end_cpu_access()
will not be called balance dma_buf_begin_cpu_access().

Fix by setting ret instead of returning.

Signed-off-by: David Lechner <david@lechnology.com>
---
 drivers/gpu/drm/tinydrm/mipi-dbi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/tinydrm/mipi-dbi.c b/drivers/gpu/drm/tinydrm/mipi-dbi.c
index c83eeb7..e10fa4b 100644
--- a/drivers/gpu/drm/tinydrm/mipi-dbi.c
+++ b/drivers/gpu/drm/tinydrm/mipi-dbi.c
@@ -183,7 +183,8 @@ static int mipi_dbi_buf_copy(void *dst, struct drm_framebuffer *fb,
 		dev_err_once(fb->dev->dev, "Format is not supported: %s\n",
 			     drm_get_format_name(fb->format->format,
 						 &format_name));
-		return -EINVAL;
+		ret = -EINVAL;
+		break;
 	}
 
 	if (import_attach)
-- 
2.7.4

Re: [PATCH] drm/tinydrm: mipi-dbi: Fix unbalanced DMA access

[Noralf Trønnes]

Den 01.08.2017 22.14, skrev David Lechner:
> If we return here and import_attach is true, then dma_buf_end_cpu_access()
> will not be called balance dma_buf_begin_cpu_access().
>
> Fix by setting ret instead of returning.
>
> Signed-off-by: David Lechner <david@lechnology.com>
> ---

Reviewed-by: Noralf Trønnes <noralf@tronnes.org>

>   drivers/gpu/drm/tinydrm/mipi-dbi.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/tinydrm/mipi-dbi.c b/drivers/gpu/drm/tinydrm/mipi-dbi.c
> index c83eeb7..e10fa4b 100644
> --- a/drivers/gpu/drm/tinydrm/mipi-dbi.c
> +++ b/drivers/gpu/drm/tinydrm/mipi-dbi.c
> @@ -183,7 +183,8 @@ static int mipi_dbi_buf_copy(void *dst, struct drm_framebuffer *fb,
>   		dev_err_once(fb->dev->dev, "Format is not supported: %s\n",
>   			     drm_get_format_name(fb->format->format,
>   						 &format_name));
> -		return -EINVAL;
> +		ret = -EINVAL;
> +		break;
>   	}
>   
>   	if (import_attach)

Re: [PATCH] drm/tinydrm: mipi-dbi: Fix unbalanced DMA access

[David Lechner]

On 08/01/2017 03:14 PM, David Lechner wrote:
> If we return here and import_attach is true, then dma_buf_end_cpu_access()
> will not be called balance dma_buf_begin_cpu_access().
> 
> Fix by setting ret instead of returning.
> 
> Signed-off-by: David Lechner <david@lechnology.com>
> ---
>   drivers/gpu/drm/tinydrm/mipi-dbi.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/tinydrm/mipi-dbi.c b/drivers/gpu/drm/tinydrm/mipi-dbi.c
> index c83eeb7..e10fa4b 100644
> --- a/drivers/gpu/drm/tinydrm/mipi-dbi.c
> +++ b/drivers/gpu/drm/tinydrm/mipi-dbi.c
> @@ -183,7 +183,8 @@ static int mipi_dbi_buf_copy(void *dst, struct drm_framebuffer *fb,
>   		dev_err_once(fb->dev->dev, "Format is not supported: %s\n",
>   			     drm_get_format_name(fb->format->format,
>   						 &format_name));
> -		return -EINVAL;
> +		ret = -EINVAL;
> +		break;
>   	}
>   
>   	if (import_attach)
> 


I just realized that the next line here can mask ret.


	if (import_attach)
		ret = dma_buf_end_cpu_access(import_attach->dmabuf,
					     DMA_FROM_DEVICE);

So, we should either ignore the return value from 
dma_buf_end_cpu_access() always or add some logic to ignore it if ret is 
already an error.

In some of the other patches I have been sending, we have the same 
situation. I those, I have opted to just ignore the return value from 
dma_buf_end_cpu_access(). e.g...


	if (import_attach)
		dma_buf_end_cpu_access(import_attach->dmabuf, DMA_FROM_DEVICE);

Is this a reasonable thing to do?

Re: [PATCH] drm/tinydrm: mipi-dbi: Fix unbalanced DMA access

[Noralf Trønnes]

Den 04.08.2017 00.41, skrev David Lechner:
> On 08/01/2017 03:14 PM, David Lechner wrote:
>> If we return here and import_attach is true, then 
>> dma_buf_end_cpu_access()
>> will not be called balance dma_buf_begin_cpu_access().
>>
>> Fix by setting ret instead of returning.
>>
>> Signed-off-by: David Lechner <david@lechnology.com>
>> ---
>>   drivers/gpu/drm/tinydrm/mipi-dbi.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/tinydrm/mipi-dbi.c 
>> b/drivers/gpu/drm/tinydrm/mipi-dbi.c
>> index c83eeb7..e10fa4b 100644
>> --- a/drivers/gpu/drm/tinydrm/mipi-dbi.c
>> +++ b/drivers/gpu/drm/tinydrm/mipi-dbi.c
>> @@ -183,7 +183,8 @@ static int mipi_dbi_buf_copy(void *dst, struct 
>> drm_framebuffer *fb,
>>           dev_err_once(fb->dev->dev, "Format is not supported: %s\n",
>>                    drm_get_format_name(fb->format->format,
>>                            &format_name));
>> -        return -EINVAL;
>> +        ret = -EINVAL;
>> +        break;
>>       }
>>         if (import_attach)
>>
>
>
> I just realized that the next line here can mask ret.
>
>
>     if (import_attach)
>         ret = dma_buf_end_cpu_access(import_attach->dmabuf,
>                          DMA_FROM_DEVICE);
>
> So, we should either ignore the return value from 
> dma_buf_end_cpu_access() always or add some logic to ignore it if ret 
> is already an error.
>
> In some of the other patches I have been sending, we have the same 
> situation. I those, I have opted to just ignore the return value from 
> dma_buf_end_cpu_access(). e.g...
>
>
>     if (import_attach)
>         dma_buf_end_cpu_access(import_attach->dmabuf, DMA_FROM_DEVICE);
>
> Is this a reasonable thing to do?

mipi_dbi_buf_copy() can be used by other rgb565 controllers, hence
the format check I think. So when that happens, it can be moved to
tinydrm-helpers.

Currently it's not possible to get an illegal format, since mipi-dbi
only supports those two formats.
Userspace can't set an illegal format, beacuse it's checked:
drm_atomic_commit -> drm_atomic_check_only -> drm_atomic_plane_check ->
drm_plane_check_pixel_format

So I think we can just leave this alone, or put the check before
import_attach if you really want to put this straight.

Noralf.

Re: [PATCH] drm/tinydrm: mipi-dbi: Fix unbalanced DMA access

[David Lechner]

On 08/04/2017 01:49 AM, Noralf Trønnes wrote:
> 
> Den 04.08.2017 00.41, skrev David Lechner:
>> On 08/01/2017 03:14 PM, David Lechner wrote:
>>> If we return here and import_attach is true, then 
>>> dma_buf_end_cpu_access()
>>> will not be called balance dma_buf_begin_cpu_access().
>>>
>>> Fix by setting ret instead of returning.
>>>
>>> Signed-off-by: David Lechner <david@lechnology.com>
>>> ---
>>>   drivers/gpu/drm/tinydrm/mipi-dbi.c | 3 ++-
>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/tinydrm/mipi-dbi.c 
>>> b/drivers/gpu/drm/tinydrm/mipi-dbi.c
>>> index c83eeb7..e10fa4b 100644
>>> --- a/drivers/gpu/drm/tinydrm/mipi-dbi.c
>>> +++ b/drivers/gpu/drm/tinydrm/mipi-dbi.c
>>> @@ -183,7 +183,8 @@ static int mipi_dbi_buf_copy(void *dst, struct 
>>> drm_framebuffer *fb,
>>>           dev_err_once(fb->dev->dev, "Format is not supported: %s\n",
>>>                    drm_get_format_name(fb->format->format,
>>>                            &format_name));
>>> -        return -EINVAL;
>>> +        ret = -EINVAL;
>>> +        break;
>>>       }
>>>         if (import_attach)
>>>
>>
>>
>> I just realized that the next line here can mask ret.
>>
>>
>>     if (import_attach)
>>         ret = dma_buf_end_cpu_access(import_attach->dmabuf,
>>                          DMA_FROM_DEVICE);
>>
>> So, we should either ignore the return value from 
>> dma_buf_end_cpu_access() always or add some logic to ignore it if ret 
>> is already an error.
>>
>> In some of the other patches I have been sending, we have the same 
>> situation. I those, I have opted to just ignore the return value from 
>> dma_buf_end_cpu_access(). e.g...
>>
>>
>>     if (import_attach)
>>         dma_buf_end_cpu_access(import_attach->dmabuf, DMA_FROM_DEVICE);
>>
>> Is this a reasonable thing to do?
> 
> mipi_dbi_buf_copy() can be used by other rgb565 controllers, hence
> the format check I think. So when that happens, it can be moved to
> tinydrm-helpers.
> 
> Currently it's not possible to get an illegal format, since mipi-dbi
> only supports those two formats.
> Userspace can't set an illegal format, beacuse it's checked:
> drm_atomic_commit -> drm_atomic_check_only -> drm_atomic_plane_check ->
> drm_plane_check_pixel_format
> 
> So I think we can just leave this alone, or put the check before
> import_attach if you really want to put this straight.
> 

I guess we can just leave it alone for now.