Re: [PATCH v2 1/4] drm/i915/dp: Link train Fallback on eDP only if fallback link BW can fit panel's native mode

[Lucas De Marchi <lucas.de.marchi@gmail.com>]

On Wed, Sep 12, 2018 at 3:55 PM Manasi Navare <manasi.d.navare@intel.com> 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.

I suspect something went bad on my laptop or the cause is something else.
I can't reproduce this problem anymore, even if I go back to old kernels.
And, in contrary to what I had previously, now I have:

# dd if=/dev/drm_dp_aux0 bs=1 | hexdump -C
...
00000070  01 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
...

Lucas De Marchi

>
> v2:
> * Send uevent if link failure on eDP unconditionally
>
> Cc: Clinton Taylor <clinton.a.taylor@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107489
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105338
> Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
> Tested-by: Alexander Wilson <alexander.wilson@ncf.edu>
> ---
>  drivers/gpu/drm/i915/intel_dp.c               | 29 +++++++++++++++++++
>  drivers/gpu/drm/i915/intel_dp_link_training.c | 26 ++++++-----------
>  2 files changed, 38 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 436c22de33b6..e4de5257cd87 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -557,6 +557,21 @@ 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)
>  {
> @@ -566,9 +581,23 @@ 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)) {
> +                       DRM_DEBUG_KMS("Retrying Link training for eDP with same parameters\n");
> +                       return 0;
> +               }
>                 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_common_rate(intel_dp),
> +                                                             lane_count >> 1)) {
> +                       DRM_DEBUG_KMS("Retrying Link training for eDP with same parameters\n");
> +                       return 0;
> +               }
>                 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 a9f40985a621..30be0e39bd5f 100644
> --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> @@ -367,22 +367,14 @@ 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;
>  }
> --
> 2.18.0
>
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-- 
Lucas De Marchi
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