[Intel-gfx] [PATCH v2 1/6] drm/i915/dp: Fix link retraining comment in intel_dp_long_pulse()

[Lyude Paul]

Reviewed-by: Lyude Paul <lyude at redhat.com>

On Mon, 2018-09-24 at 15:45 -0700, Dhinakaran Pandiyan wrote:
> Comment claims link needs to be retrained because the connected sink raised
> a long pulse to indicate link loss. If the sink did so,
> intel_dp_hotplug() would have handled link retraining. Looking at the
> logs in Bugzilla referenced in commit '3cf71bc9904d ("drm/i915: Re-apply
> Perform link quality check, unconditionally during long pulse"")', the
> issue is that the sink does not trigger an interrupt. What we want is
> ->detect() from user space to check link status and retrain. Ville's
> review for the original patch also indicates the same root cause. So,
> rewrite the comment.
> 
> v2: Patch split and rewrote comment.
> 
> Cc: Lyude Paul <lyude at redhat.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> Cc: Jan-Marek Glogowski <glogow at fbihome.de>
> References: 3cf71bc9904d ("drm/i915: Re-apply "Perform link quality check,
> unconditionally during long pulse"")
> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 13 +++----------
>  1 file changed, 3 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c
> b/drivers/gpu/drm/i915/intel_dp.c
> index 6b4c19123f2a..34c561011e7a 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -5074,16 +5074,9 @@ intel_dp_long_pulse(struct intel_connector
> *connector,
>  		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.
> +		 * Some external monitors do not signal loss of link
> +		 * synchronization with an IRQ_HPD, so force a link status
> +		 * check.
>  		 */
>  		struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)-
> >base;
>  
-- 
Cheers,
	Lyude Paul