[PATCH] drm/amd/display: fix return value of dm_dp_aux_transfer() (V2)

[S, Shirish]

On 4/20/2018 11:52 PM, Harry Wentland wrote:
> On 2018-04-17 10:56 PM, Shirish S wrote:
>> Currently the dm_dp_aux_transfer() does not parse
>> the return value of dal_ddc_service_read_dpcd_data(), which also
>> has a failure case.
>> This patch captures the same and ensures the i2c operation status is
>> sent appropriately to the drm framework.
>>
>> V2: Updated commit message.
>>
>> Signed-off-by: Shirish S <shirish.s at amd.com>
>> ---
>>   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
>> index 782491e..7ac124d 100644
>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
>> @@ -115,7 +115,11 @@ static ssize_t dm_dp_aux_transfer(struct drm_dp_aux *aux,
>>   				msg->address,
>>   				msg->buffer,
>>   				msg->size);
>> -		return read_bytes;
>> +		if (read_bytes != msg->size &&
>> +		    read_bytes >= DDC_RESULT_FAILED_OPERATION)
> This doesn't look right. We shouldn't be returning the size or error code from the same function. This will not work if we submit a read 7 or 8 bytes and get an error.
Agree,  but hope you understood the issue, to re-iterate, in case of 
failure we reuturn a +ve number(7 or 8) back from dm_dp_aux_transfer() 
leading to edid read failures later.
I have 2 suggestions:
1. change the "enum ddc_result {" to #defines of -ve error codes? or
2. make enum start with 129 (> than the max read_bytes possible)?
let me know which one would be better?
Thanks,
Regards,
Shirish S
>
> Harry
>
>> +			return -EIO;
>> +		else
>> +			return read_bytes;
>>   	case DP_AUX_I2C_WRITE:
>>   		res = dal_ddc_service_write_dpcd_data(
>>   				TO_DM_AUX(aux)->ddc_service,
>>