[Intel-gfx] [PATCH] v3 drm/i915: Re-apply "Perform link quality check, unconditionally during long pulse"

[Manasi Navare]

On Wed, Aug 08, 2018 at 10:53:35AM +0200, Jan-Marek Glogowski wrote:
> 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.

Would be nice to add in the commit message that this sink sends a
long pulse to indicate link loss, hence check link status during long pulse.

If there is a FDO bug associated with this you could also add the
Bugzilla link before Sign off tag.
But other than that this looks good to me.

Manasi

> 
> This hunk was dropped in commit c85d200e8321 ("drm/i915: Move SST
> DP link retraining into the ->post_hotplug() hook")
> 
> Signed-off-by: Jan-Marek Glogowski <glogow at fbihome.de>
> ---
>  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 8e0e14b..22b2452 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)
>  {
> @@ -4923,7 +4911,8 @@ 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);
> @@ -4982,6 +4971,22 @@ 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);
>  	}
> 
>  	/*
> @@ -5043,7 +5048,7 @@ 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;
> -- 
> 2.1.4
>