drm/i915/dp: Fix link retraining comment in intel_dp_long_pulse()

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@redhat.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Jan-Marek Glogowski <glogow@fbihome.de>
References: 3cf71bc9904d ("drm/i915: Re-apply "Perform link quality check, unconditionally during long pulse"")
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180927205735.16651-1-dhinakaran.pandiyan@intel.com
(cherry picked from commit 9ebd8202393dde9d3678c9ec162c1aa63ba17eac)
Fixes: 399334708b4f ("drm/i915: Re-apply "Perform link quality check, unconditionally during long pulse"")
Cc: stable@vger.kernel.org
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 3fae4dab295f093892491ecd010970dc7fc28128..e2a1af0a349282a18894b2fa1154cccb69746cea 100644 (file)
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -5104,16 +5104,9 @@ 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;