On Fri, 2018-08-17 at 13:40 -0700, Manasi Navare wrote:
> On Fri, Aug 17, 2018 at 04:32:09PM -0400, Lyude Paul wrote:
> > After reading the discussion so far on this patch, this sounds correct! One
> > nit
> > pick below though:
> >
> > On Wed, 2018-05-16 at 19:21 -0700, Manasi Navare wrote:
> > > This patch fixes the original commit c0cfb10d9e1de49 ("drm/i915/edp:
> > > Do not do link training fallback or prune modes on EDP") that causes
> > > a blank screen in case of certain eDP panels (Eg: seen on Dell XPS13 9350)
> > > where first link training fails and a retraining is required by falling
> > > back to lower link rate/lane count.
> > > In case of some panels they advertise higher link rate/lane count
> > > than whats required for supporting the panel's native mode.
> > > But we always link train at highest link rate/lane count for eDP
> > > and if that fails we can still fallback to lower link rate/lane count
> > > as long as the fallback link BW still fits the native mode to avoid
> > > pruning the panel's native mode yet retraining at fallback values
> > > to recover from a blank screen.
> > >
> > > Cc: Clinton Taylor <clinton.a.tay...@intel.com>
> > > Cc: Jani Nikula <jani.nik...@linux.intel.com>
> > > Cc: Ville Syrjala <ville.syrj...@linux.intel.com>
> > > Cc: Daniel Vetter <daniel.vet...@ffwll.ch>
> > > Cc: Lucas De Marchi <lucas.demar...@intel.com>
> > > Signed-off-by: Manasi Navare <manasi.d.nav...@intel.com>
> > > ---
> > > drivers/gpu/drm/i915/intel_dp.c | 25
> > > +++++++++++++++++++++++++
> > > drivers/gpu/drm/i915/intel_dp_link_training.c | 26 +++++++++-------------
> > > ----
> > > 2 files changed, 34 insertions(+), 17 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/intel_dp.c
> > > b/drivers/gpu/drm/i915/intel_dp.c
> > > index 2cc58596..7f7202a 100644
> > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > @@ -387,6 +387,21 @@ static bool intel_dp_link_params_valid(struct
> > > intel_dp
> > > *intel_dp, int link_rate,
> > > return true;
> > > }
> > >
> > > +static bool intel_dp_can_link_train_fallback_for_edp(struct intel_dp
> > > *intel_dp,
> > > + int link_rate,
> > > + uint8_t lane_count)
> > > +{
> > > + struct drm_display_mode *fixed_mode = intel_dp->attached_connector-
> > > > panel.fixed_mode;
> > >
> > > + int mode_rate, max_rate;
> > > +
> > > + mode_rate = intel_dp_link_required(fixed_mode->clock, 18);
> > > + max_rate = intel_dp_max_data_rate(link_rate, lane_count);
> > > + if (mode_rate > max_rate)
> > > + return false;
> > > +
> > > + return true;
> > > +}
> > > +
> > > int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
> > > int link_rate, uint8_t lane_count)
> > > {
> > > @@ -396,9 +411,19 @@ int intel_dp_get_link_train_fallback_values(struct
> > > intel_dp *intel_dp,
> > > intel_dp->num_common_rates,
> > > link_rate);
> > > if (index > 0) {
> > > + if (intel_dp_is_edp(intel_dp) &&
> > > + !intel_dp_can_link_train_fallback_for_edp(intel_dp,
> > > + intel_dp-
> > > > common_rates[index-1],
> > >
> > > + lane_count))
> > > + return -1;
> > > intel_dp->max_link_rate = intel_dp->common_rates[index - 1];
> > > intel_dp->max_link_lane_count = lane_count;
> > > } else if (lane_count > 1) {
> > > + if (intel_dp_is_edp(intel_dp) &&
> > > + !intel_dp_can_link_train_fallback_for_edp(intel_dp,
> > > + intel_dp_max_commo
> > > n_rate(intel_dp),
> > > + lane_count >> 1))
> > > + return -1;
> >
> > The arguments you pass to intel_dp_can_link_train_fallback_for_edp() are the
> > same ones that you assign to intel_dp->max_link_rate and intel_dp-
> > > max_link_lane_count, why not just set those latter two first then pass
> > > them to
> >
> > intel_dp_can_link_train_fallback_for_edp() afterwards?
>
> Actually I had thought of that. However if the
> intel_dp_can_link_train_fallback_for_edp()
> returns false then we dont wanna update the intel_dp->max_link_rate and
> lane_count to
> reduced fallback values.
Ahhh, that makes sense! Ignore that nitpick then :)
>
> The other concerns mentioned on this patch were about checking them against
> downclock mode
> which will be with lower refresh rate hence might fit the reduced BW. But
> currently the
> downclock mode is assigned only as part of intel_dp_drrs_support() so first we
> would
> need to may be find that in edp_init and save it as part of intel_dp or
> something.
> As well as testing against alternate mode.
> Any thoughts on that?
That sounds fine to me! It is probably a bit safer then just blindly downgrading
the link
>
> Manasi
>
> > > intel_dp->max_link_rate = intel_dp_max_common_rate(intel_dp);
> > > intel_dp->max_link_lane_count = lane_count >> 1;
> > > } else {
> > > diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c
> > > b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > > index 3fcaa98..6673975 100644
> > > --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> > > +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > > @@ -335,22 +335,14 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
> > > return;
> > >
> > > failure_handling:
> > > - /* Dont fallback and prune modes if its eDP */
> > > - if (!intel_dp_is_edp(intel_dp)) {
> > > - DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Link Training failed at link
> > > rate = %d, lane count = %d",
> > > - intel_connector->base.base.id,
> > > - intel_connector->base.name,
> > > - intel_dp->link_rate, intel_dp->lane_count);
> > > - if (!intel_dp_get_link_train_fallback_values(intel_dp,
> > > - intel_dp-
> > > > link_rate,
> > >
> > > - intel_dp-
> > > > lane_count))
> > >
> > > - /* Schedule a Hotplug Uevent to userspace to start
> > > modeset */
> > > - schedule_work(&intel_connector->modeset_retry_work);
> > > - } else {
> > > - DRM_ERROR("[CONNECTOR:%d:%s] Link Training failed at link rate =
> > > %d, lane count = %d",
> > > - intel_connector->base.base.id,
> > > - intel_connector->base.name,
> > > - intel_dp->link_rate, intel_dp->lane_count);
> > > - }
> > > + DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Link Training failed at link rate = %d,
> > > lane count = %d",
> > > + intel_connector->base.base.id,
> > > + intel_connector->base.name,
> > > + intel_dp->link_rate, intel_dp->lane_count);
> > > + if (!intel_dp_get_link_train_fallback_values(intel_dp,
> > > + intel_dp->link_rate,
> > > + intel_dp->lane_count))
> > > + /* Schedule a Hotplug Uevent to userspace to start modeset */
> > > + schedule_work(&intel_connector->modeset_retry_work);
> > > return;
> > > }
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