Re: [PATCH 1/4] drm/radeon/dp: handle zero sized i2c over aux transactions

[Alex Deucher <alexdeucher@gmail.com>]

On Mon, Apr 7, 2014 at 3:57 AM, Jani Nikula <jani.nikula@linux.intel.com> wrote:
> On Fri, 04 Apr 2014, Alex Deucher <alexdeucher@gmail.com> wrote:
>> Needed for proper i2c over aux handling for certain
>> monitors and configurations (e.g., dp bridges or
>> adapters).
>>
>> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
>> ---
>>  drivers/gpu/drm/radeon/atombios_dp.c | 15 +++++++++++----
>>  1 file changed, 11 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/radeon/atombios_dp.c b/drivers/gpu/drm/radeon/atombios_dp.c
>> index 8b0ab17..e914008 100644
>> --- a/drivers/gpu/drm/radeon/atombios_dp.c
>> +++ b/drivers/gpu/drm/radeon/atombios_dp.c
>> @@ -143,6 +143,7 @@ static int radeon_process_aux_ch(struct radeon_i2c_chan *chan,
>>  }
>>
>>  #define HEADER_SIZE 4
>> +#define BARE_ADDRESS_SIZE 3
>>
>>  static ssize_t
>>  radeon_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>> @@ -160,13 +161,16 @@ radeon_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>>       tx_buf[0] = msg->address & 0xff;
>>       tx_buf[1] = msg->address >> 8;
>>       tx_buf[2] = msg->request << 4;
>> -     tx_buf[3] = msg->size - 1;
>> +     tx_buf[3] = msg->size ? (msg->size - 1) : 0;
>>
>>       switch (msg->request & ~DP_AUX_I2C_MOT) {
>>       case DP_AUX_NATIVE_WRITE:
>>       case DP_AUX_I2C_WRITE:
>>               tx_size = HEADER_SIZE + msg->size;
>> -             tx_buf[3] |= tx_size << 4;
>> +             if (msg->size == 0)
>> +                     tx_buf[3] |= BARE_ADDRESS_SIZE << 4;
>> +             else
>> +                     tx_buf[3] |= tx_size << 4;
>>               memcpy(tx_buf + HEADER_SIZE, msg->buffer, msg->size);
>>               ret = radeon_process_aux_ch(chan,
>>                                           tx_buf, tx_size, NULL, 0, delay, &ack);
>
> I think your tz_size and tx_buf[3] are confused. Shouldn't you only send
> 3 bytes of tx_buf when msg->size == 0?
>
> Disclaimer, I don't know anything about your hw and all that... :)

It doesn't really matter.  The hw only cares about the size specified
in tx_buf[3]. tx_size is only used to determine how much data to the
buffer used by the atom table.  We end up copying an extra byte that
never gets used.  I suppose I should fix it up for clarify.

Alex

>
> BR,
> Jani.
>
>
>> @@ -177,7 +181,10 @@ radeon_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>>       case DP_AUX_NATIVE_READ:
>>       case DP_AUX_I2C_READ:
>>               tx_size = HEADER_SIZE;
>> -             tx_buf[3] |= tx_size << 4;
>> +             if (msg->size == 0)
>> +                     tx_buf[3] |= BARE_ADDRESS_SIZE << 4;
>> +             else
>> +                     tx_buf[3] |= tx_size << 4;
>>               ret = radeon_process_aux_ch(chan,
>>                                           tx_buf, tx_size, msg->buffer, msg->size, delay, &ack);
>>               break;
>> @@ -186,7 +193,7 @@ radeon_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>>               break;
>>       }
>>
>> -     if (ret > 0)
>> +     if (ret >= 0)
>>               msg->reply = ack >> 4;
>>
>>       return ret;
>> --
>> 1.8.3.1
>>
>
> --
> Jani Nikula, Intel Open Source Technology Center