[PATCH] drm/msm/dp: always add fail-safe mode into connector mode list

[Kuogee Hsieh]

On 1/24/2022 1:04 PM, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2022-01-24 12:46:10)
>> Some of DP link compliant test expects to return fail-safe mode
>> if prefer detailed timing mode can not be supported by mainlink's
>> lane and rate after link training. Therefore add fail-safe mode
>> into connector mode list as backup mode. This patch fixes test
>> case 4.2.2.1.
>>
>> Signed-off-by: Kuogee Hsieh <quic_khsieh at quicinc.com>
> Any Fixes tag? I also wonder why this isn't pushed into the DP core code
> somehow. Wouldn't every device need to add a 640x480 mode by default?

Original test case 4.2.2.1 always passed until we did firmware upgrade 
of our compliance test tester (Unigraph) recently.

The new firmware of tester use newer edid contains 1080p with 145.7 mhz 
which can not be supported by 2 lanes with 1.6G rate. Hence we failed 
this test case.

After discuss with Vendor, they claims we have to return fail-safe mode 
if prefer detailed timing mode can not be supported.

I think would be good to add fail-safe mode into connector mode list.




> we just run into this problem recently.
>> ---
>>   drivers/gpu/drm/msm/dp/dp_panel.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/msm/dp/dp_panel.c b/drivers/gpu/drm/msm/dp/dp_panel.c
>> index 3b02922..7743b45 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_panel.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_panel.c
>> @@ -221,6 +221,11 @@ int dp_panel_read_sink_caps(struct dp_panel *dp_panel,
>>                  if (drm_add_modes_noedid(connector, 640, 480))
>>                          drm_set_preferred_mode(connector, 640, 480);
>>                  mutex_unlock(&connector->dev->mode_config.mutex);
>> +       } else {
>> +               /* always add fail-safe mode as backup mode */
>> +               mutex_lock(&connector->dev->mode_config.mutex);
>> +               drm_add_modes_noedid(connector, 640, 480);
>> +               mutex_unlock(&connector->dev->mode_config.mutex);
>>          }
>>
>>          if (panel->aux_cfg_update_done) {
>> --
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