Re: [PATCH 5/6] drm: zynqmp_dp: Optionally ignore DPCD errors

[Sean Anderson <sean.anderson@linux.dev>]

On 3/18/24 13:47, Laurent Pinchart wrote:
> Hi Sean,
> 
> Thank you for the patch.
> 
> On Fri, Mar 15, 2024 at 07:09:15PM -0400, Sean Anderson wrote:
>> When testing, it's convenient to be able to ignore DPCD errors if there
>> is test equipment which can't emulate a DPRX connected to the output.
>> Add some (currently-unused) options to ignore these errors and just
>> reconfigure our internal registers as we usually would.
> 
> This seems to be a problem that is not limited to the ZynqMP DP.
> Wouldn't it be better to solve it in the DRM DP DPCD helpers instead ?
> You could expose a parameter on the AUX bus in debugfs to ignore errors,
> and cause the drm_dp_dpcd_write*() functions to return 0.

I think this is probably the easiest thing. I'll add this for v2.

I think something similar might be nice for HPD events (instead of always
ignoring them in test mode). This would make it easier to add DPRX-driven
testing in the future.

--Sean

>> Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
>> ---
>> 
>>  drivers/gpu/drm/xlnx/zynqmp_dp.c | 37 ++++++++++++++++++++------------
>>  1 file changed, 23 insertions(+), 14 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
>> index 24043847dab4..040f7b88ee51 100644
>> --- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
>> +++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
>> @@ -628,6 +628,7 @@ static void zynqmp_dp_adjust_train(struct zynqmp_dp *dp,
>>   * zynqmp_dp_update_vs_emph - Update the training values
>>   * @dp: DisplayPort IP core structure
>>   * @train_set: A set of training values
>> + * @ignore_dpcd: Ignore DPCD errors
>>   *
>>   * Update the training values based on the request from sink. The mapped values
>>   * are predefined, and values(vs, pe, pc) are from the device manual.
>> @@ -635,15 +636,19 @@ static void zynqmp_dp_adjust_train(struct zynqmp_dp *dp,
>>   * Return: 0 if vs and emph are updated successfully, or the error code returned
>>   * by drm_dp_dpcd_write().
>>   */
>> -static int zynqmp_dp_update_vs_emph(struct zynqmp_dp *dp, u8 *train_set)
>> +static int zynqmp_dp_update_vs_emph(struct zynqmp_dp *dp, u8 *train_set,
>> +				    bool ignore_dpcd)
>>  {
>>  	unsigned int i;
>>  	int ret;
>>  
>>  	ret = drm_dp_dpcd_write(&dp->aux, DP_TRAINING_LANE0_SET, train_set,
>>  				dp->mode.lane_cnt);
>> -	if (ret < 0)
>> -		return ret;
>> +	if (ret < 0) {
>> +		if (!ignore_dpcd)
>> +			return ret;
>> +		dev_warn(dp->dev, "failed to update vs/emph\n");
>> +	}
>>  
>>  	for (i = 0; i < dp->mode.lane_cnt; i++) {
>>  		u32 reg = ZYNQMP_DP_SUB_TX_PHY_PRECURSOR_LANE_0 + i * 4;
>> @@ -692,7 +697,7 @@ static int zynqmp_dp_link_train_cr(struct zynqmp_dp *dp)
>>  	 * So, This loop should exit before 512 iterations
>>  	 */
>>  	for (max_tries = 0; max_tries < 512; max_tries++) {
>> -		ret = zynqmp_dp_update_vs_emph(dp, dp->train_set);
>> +		ret = zynqmp_dp_update_vs_emph(dp, dp->train_set, false);
>>  		if (ret)
>>  			return ret;
>>  
>> @@ -757,7 +762,7 @@ static int zynqmp_dp_link_train_ce(struct zynqmp_dp *dp)
>>  		return ret;
>>  
>>  	for (tries = 0; tries < DP_MAX_TRAINING_TRIES; tries++) {
>> -		ret = zynqmp_dp_update_vs_emph(dp, dp->train_set);
>> +		ret = zynqmp_dp_update_vs_emph(dp, dp->train_set, false);
>>  		if (ret)
>>  			return ret;
>>  
>> @@ -785,11 +790,12 @@ static int zynqmp_dp_link_train_ce(struct zynqmp_dp *dp)
>>   * @lane_cnt: The number of lanes to use
>>   * @enhanced: Use enhanced framing
>>   * @downspread: Enable spread-spectrum clocking
>> + * @ignore_dpcd: Ignore DPCD errors; useful for testing
>>   *
>>   * Return: 0 on success, or -errno on failure
>>   */
>>  static int zynqmp_dp_setup(struct zynqmp_dp *dp, u8 bw_code, u8 lane_cnt,
>> -			   bool enhanced, bool downspread)
>> +			   bool enhanced, bool downspread, bool ignore_dpcd)
>>  {
>>  	u32 reg;
>>  	u8 aux_lane_cnt = lane_cnt;
>> @@ -812,21 +818,24 @@ static int zynqmp_dp_setup(struct zynqmp_dp *dp, u8 bw_code, u8 lane_cnt,
>>  
>>  	ret = drm_dp_dpcd_writeb(&dp->aux, DP_LANE_COUNT_SET, aux_lane_cnt);
>>  	if (ret < 0) {
>> -		dev_err(dp->dev, "failed to set lane count\n");
>> -		return ret;
>> +		dev_warn(dp->dev, "failed to set lane count\n");
>> +		if (!ignore_dpcd)
>> +			return ret;
>>  	}
>>  
>>  	ret = drm_dp_dpcd_writeb(&dp->aux, DP_MAIN_LINK_CHANNEL_CODING_SET,
>>  				 DP_SET_ANSI_8B10B);
>>  	if (ret < 0) {
>> -		dev_err(dp->dev, "failed to set ANSI 8B/10B encoding\n");
>> -		return ret;
>> +		dev_warn(dp->dev, "failed to set ANSI 8B/10B encoding\n");
>> +		if (!ignore_dpcd)
>> +			return ret;
>>  	}
>>  
>>  	ret = drm_dp_dpcd_writeb(&dp->aux, DP_LINK_BW_SET, bw_code);
>>  	if (ret < 0) {
>> -		dev_err(dp->dev, "failed to set DP bandwidth\n");
>> -		return ret;
>> +		dev_warn(dp->dev, "failed to set DP bandwidth\n");
>> +		if (!ignore_dpcd)
>> +			return ret;
>>  	}
>>  
>>  	zynqmp_dp_write(dp, ZYNQMP_DP_LINK_BW_SET, bw_code);
>> @@ -860,7 +869,7 @@ static int zynqmp_dp_train(struct zynqmp_dp *dp)
>>  
>>  	ret = zynqmp_dp_setup(dp, dp->mode.bw_code, dp->mode.lane_cnt,
>>  			      drm_dp_enhanced_frame_cap(dp->dpcd),
>> -			      dp->dpcd[3] & 0x1);
>> +			      dp->dpcd[3] & 0x1, false);
>>  	if (ret)
>>  		return ret;
>>  
>> @@ -877,7 +886,7 @@ static int zynqmp_dp_train(struct zynqmp_dp *dp)
>>  	ret = drm_dp_dpcd_writeb(&dp->aux, DP_TRAINING_PATTERN_SET,
>>  				 DP_TRAINING_PATTERN_DISABLE);
>>  	if (ret < 0) {
>> -		dev_err(dp->dev, "failed to disable training pattern\n");
>> +		dev_warn(dp->dev, "failed to disable training pattern\n");
>>  		return ret;
>>  	}
>>  	zynqmp_dp_write(dp, ZYNQMP_DP_TRAINING_PATTERN_SET,
> 


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