[Intel-gfx] [PATCH] drm/i915: Don't recheck link status for eDP display.

[Rodrigo Vivi]

Puthikorn,

could you please test the patch Manasi had pointed out [1] to see if that
solves your issue instead of your patch?

If that one solves it you put a Tested-by on that one to help that getting merged.

If that is not the case so we need to hunt down PSR2 bugs that are killing the link status.

[1]: https://patchwork.freedesktop.org/patch/178035/

Thanks,
Rodrigo.

On Tue, Oct 17, 2017 at 11:31:46PM +0000, Puthikorn Voravootivat wrote:
> + Vathsala for PSR related code.
> 
> On Tue, Oct 17, 2017 at 4:29 PM, Manasi Navare
> <manasi.d.navare at intel.com> wrote:
> > On Tue, Oct 17, 2017 at 03:46:00PM -0700, Puthikorn Voravootivat wrote:
> >> I tried  https://patchwork.freedesktop.org/series/30670/ but it doesn't work.
> >>
> >> > When you see the display blinking, do you know for sure that drm_dp_channel_eq_ok() returns false?
> >> Yes. Repro is running "modetest" while PSR is on (easier to repro with
> >> PSR2 but PSR1 is fine too)
> >>
> >> > lane_align = dp_link_status(link_status,
> >> >    DP_LANE_ALIGN_STATUS_UPDATED);
> >> > if ((lane_align & DP_INTERLANE_ALIGN_DONE) == 0)
> >> >    return false;
> >>
> >> I always got lane_align = 128 (DP_LINK_STATUS_UPDATED)
> >> So drm_dp_channel_eq_ok() always return false.
> >
> > Hmm, it looks like there is a bug somewhere else that is causing the
> > link status to get updated and bit LINK_STATUS_UPDATED from LANE_ALIGN_STATUS_UPDATED register
> > is not being read so not being cleared causing the link to be retrained again.
> >
> > So I still feel that this patch is a workaround for another bug in the PSR code.
> > But I will let others comment on this.
> >
> > Regards
> > Manasi
> >
> >>
> >> If I disable PSR, drm_dp_channel_eq_ok() will return true and no
> >> blinking occurs.
> >>
> >> On Tue, Oct 17, 2017 at 2:21 PM, Manasi Navare
> >> <manasi.d.navare at intel.com> wrote:
> >> > On Tue, Oct 17, 2017 at 02:01:56PM -0700, Puthikorn Voravootivat wrote:
> >> >> intel_dp_long_pulse() is always checking link status because
> >> >> there has been known issues of link loss triggerring long pulse.
> >> >>
> >> >> However this is not needed for eDP display since we won't have
> >> >> link loss for internal display. Also there are reports that
> >> >> screens are flickering during link status check. (repro by
> >> >> running modetest command repeatedly)
> >> >>
> >> >> Signed-off-by: Puthikorn Voravootivat <puthik at chromium.org>
> >> >> ---
> >> >>  drivers/gpu/drm/i915/intel_dp.c | 7 ++++++-
> >> >>  1 file changed, 6 insertions(+), 1 deletion(-)
> >> >>
> >> >> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> >> >> index 4b65cf137f79..75a77ef257e2 100644
> >> >> --- a/drivers/gpu/drm/i915/intel_dp.c
> >> >> +++ b/drivers/gpu/drm/i915/intel_dp.c
> >> >> @@ -4763,7 +4763,8 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
> >> >>                */
> >> >>               status = connector_status_disconnected;
> >> >>               goto out;
> >> >> -     } else {
> >> >> +     } else if (status != connector_status_connected ||
> >> >> +                intel_encoder->type != INTEL_OUTPUT_EDP) {
> >> >>               /*
> >> >>                * If display is now connected check links status,
> >> >>                * there has been known issues of link loss triggerring
> >> >> @@ -4775,6 +4776,10 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
> >> >>                * going back up soon after. And once that happens we must
> >> >>                * retrain the link to get a picture. That's in case no
> >> >>                * userspace component reacted to intermittent HPD dip.
> >> >> +              *
> >> >> +              * Skip checking links status for connected eDP display.
> >> >> +              * There are known issues of display blinking during checking
> >> >> +              * link status and we don't have link loss for internal display.
> >> >>                */
> >> >
> >> > Inside intel_dp_check_link_status(), it actually checks if link status is good by
> >> > checking both clock recovery and Channel EQ bits in DPCD, only then it will retrain.
> >> > So in case of eDP panel, if there is no link loss then it should always return link
> >> > status as good and not retrain.
> >> > So IMHO I dont think we need to explicitly avoid this for eDP.
> >> >
> >> > When you see the display blinking, do you know for sure that drm_dp_channel_eq_ok() returns false?
> >> > Also look at this patch: https://patchwork.freedesktop.org/series/30670/
> >> > This makes sure none of the eDP training parameters change unless link is bad. So with this patch, if the
> >> > link is good then it should never retrain even in intel_dp_check_link_status() for eDP.
> >> >
> >> > Manasi
> >> >>               intel_dp_check_link_status(intel_dp);
> >> >>       }
> >> >> --
> >> >> 2.15.0.rc0.271.g36b669edcc-goog
> >> >>
> >> >> _______________________________________________
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> >> >> Intel-gfx at lists.freedesktop.org
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