On Sat, Aug 25, 2018 at 03:10:35PM -0400, Lyude Paul wrote:
> From: Jan-Marek Glogowski <glogow@xxxxxxxxxx>
>
> This re-applies the workaround for "some DP sinks, [which] are a
> little nuts" from commit 1a36147bb939 ("drm/i915: Perform link
> quality check unconditionally during long pulse").
> It makes the secondary AOC E2460P monitor connected via DP to an
> acer Veriton N4640G usable again.
>
> This hunk was dropped in commit c85d200e8321 ("drm/i915: Move SST
> DP link retraining into the ->post_hotplug() hook")
>
> Fixes: c85d200e8321 ("drm/i915: Move SST DP link retraining into the ->post_hotplug() hook")
> [Cleaned up commit message, added stable cc]
> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> Signed-off-by: Jan-Marek Glogowski <glogow@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
> Resending this to update patchwork; will push in a little bit
>
> drivers/gpu/drm/i915/intel_dp.c | 33 +++++++++++++++++++--------------
> 1 file changed, 19 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index b3f6f04c3c7d..db8515171270 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -4333,18 +4333,6 @@ intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
> return !drm_dp_channel_eq_ok(link_status, intel_dp->lane_count);
> }
>
> -/*
> - * If display is now connected check links status,
> - * there has been known issues of link loss triggering
> - * long pulse.
> - *
> - * Some sinks (eg. ASUS PB287Q) seem to perform some
> - * weird HPD ping pong during modesets. So we can apparently
> - * end up with HPD going low during a modeset, and then
> - * 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.
> - */
> int intel_dp_retrain_link(struct intel_encoder *encoder,
> struct drm_modeset_acquire_ctx *ctx)
> {
> @@ -5031,7 +5019,8 @@ intel_dp_unset_edid(struct intel_dp *intel_dp)
> }
>
> static int
> -intel_dp_long_pulse(struct intel_connector *connector)
> +intel_dp_long_pulse(struct intel_connector *connector,
> + struct drm_modeset_acquire_ctx *ctx)
> {
> struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
> struct intel_dp *intel_dp = intel_attached_dp(&connector->base);
> @@ -5090,6 +5079,22 @@ intel_dp_long_pulse(struct intel_connector *connector)
> */
> status = connector_status_disconnected;
> goto out;
> + } else {
> + /*
> + * If display is now connected check links status,
> + * there has been known issues of link loss triggering
> + * long pulse.
> + *
> + * Some sinks (eg. ASUS PB287Q) seem to perform some
> + * weird HPD ping pong during modesets. So we can apparently
> + * end up with HPD going low during a modeset, and then
> + * 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.
> + */
> + struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
> +
> + intel_dp_retrain_link(encoder, ctx);
We should really have a comment here that this is purely duct tape for
sinks that fail to signal a hpd when the link goes bad (either that or
we fail to process the hpd correctly).
I suppose a better way to do this hack would be to do the link quality
check at the end of modeset, or from a delayed work. As is this depends
on userspace/fbdev doing an explicit probe after the modeset which seems
pretty fragile.
> }
>
> /*
> @@ -5151,7 +5156,7 @@ intel_dp_detect(struct drm_connector *connector,
> return ret;
> }
>
> - status = intel_dp_long_pulse(intel_dp->attached_connector);
> + status = intel_dp_long_pulse(intel_dp->attached_connector, ctx);
> }
>
> intel_dp->detect_done = false;
> --
> 2.17.1
>
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--
Ville Syrjälä
Intel
