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

[Alex Deucher]

On Wed, Dec 14, 2022 at 5:25 PM Alex Hung <alex.hung at amd.com> wrote:
>
>
>
> On 2022-12-14 14:54, Alex Deucher wrote:
> > On Wed, Dec 14, 2022 at 4:50 PM Alex Hung <alex.hung at amd.com> wrote:
> >>
> >>
> >>
> >> 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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.freedesktop.org%2Fdrm%2Figt-gpu-tools%2F-%2Fblob%2Fmaster%2Ftests%2Fkms_bw.c%23L197&data=05%7C01%7Calex.hung%40amd.com%7Cee0c28620f2447f13a8f08dade1dc0bc%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638066516634100466%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=mx33srt3RgcA4ZklYVXom9ZQklJjWmcywEtb4qJQVBQ%3D&reserved=0)
> >>
> >> 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.
> >
> > Why does sleep vs delay make a difference?  Is there some race that we
> > are not locking against?
> >
> > Alex
> >
>
> That was my original thought but I did not find any previously. I will
> investigate it again.
>
> If mdelay(>4) isn't usable on other platforms, is it an option to use
> mdelay on x86_64 only and keep msleep on other platforms or just remove
> the msleep for other platforms, something like
>
> -                       msleep(60);
> +#ifdef CONFIG_X86_64
> +                       mdelay(60);
> +#endif

That's pretty ugly.  I'd rather try and resolve the root cause.  How
important is the IGT test?  What does it do?  Is the test itself
correct?

Alex


>
>
> >>
> >>>
> >>>>
> >>>> 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
> >>>>