On Wed, May 27, 2020 at 01:54:27PM -0700, Manasi Navare wrote:
> On Wed, May 27, 2020 at 11:00:22PM +0300, Stanislav Lisovskiy wrote:
> > First of all *_needs_link_retraining function should return
> > false is link_train is set to true but not false.
> >
> > Also if we detect channel eq problem when checking mst status
> > we simply bail out, without setting link_train to false again,
> > which might end up in a situation that we don't do link retraining
> > when needed.
> >
> > There were some issues, when we had several problems with dp mst
> > and at the same time the log was floode by messages about
> > "channel eq not ok, need retraining" however the actual training
> > seems to be never done.
> >
> > Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/display/intel_dp.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 1768731678a1..9288dc1f8914 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -5627,6 +5627,7 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
> > drm_dbg_kms(&i915->drm,
> > "channel EQ not ok, retraining\n");
> > need_retrain = true;
> > + intel_dp->link_trained = false;
> > }
> >
> > drm_dbg_kms(&i915->drm, "got esi %3ph\n", esi);
> > @@ -5654,7 +5655,7 @@ intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
> > {
> > u8 link_status[DP_LINK_STATUS_SIZE];
> >
> > - if (!intel_dp->link_trained)
> > + if (intel_dp->link_trained)
>
> This is not correct. Since link_trained is set when link training is completed as part of a
> complete modeset. If link training is not done, like at hotplug, then in that case we should
> not retrain since the pipe has not been configured for this new hotplug and link training
> has not been done.
>
Ok, I was confusing the link training and retraining - assuming those are same procedure.
So we can't retrain until the training has been completed.
Thanks for clarification - will dig further then.
> Retraining is expected to happen only in cases where there is a short pulse or a spurious long pulse
> when link training through modeset is already complete and hence the old logic of returnin a false
> when !intel_dp->link_trained is correct.
Yes, that is the scenario which I was suspecting to be happening in our recent MST failures.
We sometimes get a lot of short pulses requiring rettraining however it doesn't happen in practice.
Stan
>
> Regards
> Manasi
>
> > return false;
> >
> > /*
> > --
> > 2.24.1.485.gad05a3d8e5
> >
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