Re: [PATCH v3] ucsi_ccg: Refine the UCSI Interrupt handling

[Haotien Hsu <haotienh@nvidia.com>]

On 1/6/23 16:10, Greg Kroah-Hartman wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Tue, Jan 03, 2023 at 04:15:31PM +0800, Haotien Hsu wrote:
>> From: Sing-Han Chen <singhanc@nvidia.com>
>>
>> For the CCGx, when the OPM field in the INTR_REG is cleared, then the
>> CCI data in the PPM is reset.
>>
>> To align with the CCGx UCSI interface guide, this patch updates the
>> driver to copy CCI and MESSAGE_IN before clearing UCSI interrupt.
>> When a new command is sent, the driver will clear the old CCI and
>> MESSAGE_IN copy.
>>
>> Finally, clear UCSI_READ_INT before calling complete() to ensure that
>> the ucsi_ccg_sync_write() would wait for the interrupt handling to
>> complete.
>> It prevents the driver from resetting CCI prematurely.
>>
>> Signed-off-by: Sing-Han Chen <singhanc@nvidia.com>
>> Signed-off-by: Haotien Hsu <haotienh@nvidia.com>
>> ---
>> V1->V2
>> - Fix uninitialized symbol 'cci'
>> v2->v3
>> - Remove wrong Reported-by tags
>> ---
>>   drivers/usb/typec/ucsi/ucsi_ccg.c | 86 ++++++++++++++++++++++++++++---
>>   1 file changed, 79 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/usb/typec/ucsi/ucsi_ccg.c b/drivers/usb/typec/ucsi/ucsi_ccg.c
>> index eab3012e1b01..b35a3a97c9fb 100644
>> --- a/drivers/usb/typec/ucsi/ucsi_ccg.c
>> +++ b/drivers/usb/typec/ucsi/ucsi_ccg.c
>> @@ -192,6 +192,12 @@ struct ucsi_ccg_altmode {
>>        bool checked;
>>   } __packed;
>>
>> +#define CCGX_MESSAGE_IN_MAX 4
>> +struct op_region {
>> +     u32 cci;
>> +     u32 message_in[CCGX_MESSAGE_IN_MAX];
>> +};
>> +
>>   struct ucsi_ccg {
>>        struct device *dev;
>>        struct ucsi *ucsi;
>> @@ -222,6 +228,9 @@ struct ucsi_ccg {
>>        bool has_multiple_dp;
>>        struct ucsi_ccg_altmode orig[UCSI_MAX_ALTMODES];
>>        struct ucsi_ccg_altmode updated[UCSI_MAX_ALTMODES];
>> +
>> +     spinlock_t op_lock;
> 
> What does this lock protect?  Please document that so that we can verify
> if this really is a correct change _AND_ so we know what future changes
> need to take the lock or not.
> 

/* This spinlock protects op_data which includes CCI and MESSAGE_IN that
  * will be updated in ISR */
spinlock_t op_lock;

I will add this comment into v4.

>> +     struct op_region op_data;
>>   };
>>
>>   static int ccg_read(struct ucsi_ccg *uc, u16 rab, u8 *data, u32 len)
>> @@ -305,12 +314,57 @@ static int ccg_write(struct ucsi_ccg *uc, u16 rab, const u8 *data, u32 len)
>>        return 0;
>>   }
>>
>> +static void ccg_op_region_read(struct ucsi_ccg *uc, unsigned int offset,
>> +             void *val, size_t val_len)
>> +{
>> +     struct op_region *data = &uc->op_data;
>> +
>> +     spin_lock(&uc->op_lock);
>> +     if (offset == UCSI_CCI)
>> +             memcpy(val, &data->cci, val_len);
>> +     else if (offset == UCSI_MESSAGE_IN)
>> +             memcpy(val, &data->message_in, val_len);
>> +     spin_unlock(&uc->op_lock);
>> +}
>> +
>> +static void ccg_op_region_update(struct ucsi_ccg *uc, u32 cci)
>> +{
>> +     u16 reg = CCGX_RAB_UCSI_DATA_BLOCK(UCSI_MESSAGE_IN);
>> +     struct op_region *data = &uc->op_data;
>> +     u32 message_in[CCGX_MESSAGE_IN_MAX];
>> +
>> +     if (UCSI_CCI_LENGTH(cci))
>> +             if (ccg_read(uc, reg, (void *)&message_in,
>> +                                     sizeof(message_in))) {
>> +                     dev_err(uc->dev, "failed to read MESSAGE_IN\n");
> 
> What can userspace do with this error?  Will it be repeated a lot?
> 

If driver is okay to read CCI but failed to read MESSAGE_IN, it's an
critical error in CCGx and in this situation, this log could repeat a lot.
We don't seem to have a good way to help this situation from userspace.

In our case, the failure on ccg_read() is mostly because of the I2C
issue. When there is an I2C issue between CCGx & Tegra, the failure is
more likely happening in the earlier stage (e.g., INTR read or CCI read).

Please let me know if you have more questions and concerns.

> thanks,
> 
> greg k-h
>