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

[Alex Deucher]

On Mon, Apr 7, 2014 at 9:24 AM, Alex Deucher <alexdeucher at gmail.com> wrote:
> On Mon, Apr 7, 2014 at 3:57 AM, Jani Nikula <jani.nikula at linux.intel.com> wrote:
>> On Fri, 04 Apr 2014, Alex Deucher <alexdeucher at 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 at 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.

Actually, I was wrong.  We need all 4 bytes of the tx_buf, but the hw
only sends 3 based on the size specified in tx_buf[3]. so the code is
correct as is.

Alex

>
> 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