[PATCH 05/18] drm/amd/display: Use mdelay to avoid crashes

[Alex Hung]

On 2022-12-14 13:48, Alex Deucher wrote:
> On Wed, Dec 14, 2022 at 3:22 PM Aurabindo Pillai
> <aurabindo.pillai at amd.com> wrote:
>>
>> From: Alex Hung <alex.hung at amd.com>
>>
>> [Why]
>> When running IGT kms_bw test with DP monitor, some systems crash from
>> msleep no matter how long or short the time is.
>>
>> [How]
>> To replace msleep with mdelay.
> 
> Can you provide a bit more info about the crash?  A lot of platforms
> don't support delay larger than 2-4ms so this change will generate
> errors on ARM and possibly other platforms.
> 
> Alex

The msleep was introduced in eec3303de3378 for non-compliant display 
port monitors but IGT's kms_bw test can cause a recent h/w to hang at 
msleep(60) when calling "igt_remove_fb" in IGT 
(https://gitlab.freedesktop.org/drm/igt-gpu-tools/-/blob/master/tests/kms_bw.c#L197)

It is possible to workaround this by reversing order of 
igt_remove_fb(&buffer[i]), as the following example:

   igt_create_color_fb with the order buffer[0], buffer[1], buffer[2]

Hangs:
   igt_remove_fb with the order buffer[0], buffer[1], buffer[2]

No hangs:
   igt_remove_fb with the reversed order buffer[2], buffer[1], buffer[0]

However, IGT simply exposes the problem and it makes more sense to stop 
the hang from occurring.

I also tried to remove the msleep completely and it also work, but I 
didn't want to break the fix for the original problematic hardware 
configuration.

> 
>>
>> Acked-by: Aurabindo Pillai <aurabindo.pillai at amd.com>
>> Signed-off-by: Alex Hung <alex.hung at amd.com>
>> Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira at amd.com>
>> ---
>>   drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c b/drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c
>> index 913a1fe6b3da..e6251ccadb70 100644
>> --- a/drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c
>> +++ b/drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c
>> @@ -1215,7 +1215,7 @@ void dce110_blank_stream(struct pipe_ctx *pipe_ctx)
>>                           * After output is idle pattern some sinks need time to recognize the stream
>>                           * has changed or they enter protection state and hang.
>>                           */
>> -                       msleep(60);
>> +                       mdelay(60);
>>                  } else if (pipe_ctx->stream->signal == SIGNAL_TYPE_EDP) {
>>                          if (!link->dc->config.edp_no_power_sequencing) {
>>                                  /*
>> --
>> 2.39.0
>>