Re: [PATCH 4/4] drm/i915: force full detect on sink count change

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On 9/1/2015 4:12 PM, Jani Nikula wrote:
On Thu, 27 Aug 2015, Sivakumar Thulasimani <sivakumar.thulasimani@xxxxxxxxx> wrote:
From: "Thulasimani,Sivakumar" <sivakumar.thulasimani@xxxxxxxxx>

This patch checks for changes in sink count between short pulse
hpds and forces full detect when there is a change.

This will allow both detection of hotplug and unplug of panels
through dongles that give only short pulse for such events.

v2: changed variable type from u8 to bool (Jani)
     return immediately if perform_full_detect is set(Siva)
The general idea LGTM, however see below.

Signed-off-by: Sivakumar Thulasimani <sivakumar.thulasimani@xxxxxxxxx>
---
  drivers/gpu/drm/i915/intel_dp.c |   27 ++++++++++++++++++++++-----
  1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 834f513..279e52c 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -4370,26 +4370,39 @@ go_again:
   *  4. Check link status on receipt of hot-plug interrupt
   */
  static void
-intel_dp_check_link_status(struct intel_dp *intel_dp)
+intel_dp_check_link_status(struct intel_dp *intel_dp, bool *perform_full_detect)
  {
  	struct drm_device *dev = intel_dp_to_dev(intel_dp);
  	struct intel_encoder *intel_encoder = &dp_to_dig_port(intel_dp)->base;
  	struct intel_crtc *crtc =
  		to_intel_crtc(dp_to_dig_port(intel_dp)->base.base.crtc);
  	u8 sink_irq_vector;
+	u8 old_sink_count = intel_dp->sink_count;
+	bool ret;
  	u8 link_status[DP_LINK_STATUS_SIZE];
WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex)); + *perform_full_detect = false;
+
  	/* Try to read receiver status if the link appears to be up */
  	if (!intel_dp_get_link_status(intel_dp, link_status)) {
  		return;
  	}
- /* Now read the DPCD to see if it's actually running */
-	if (!intel_dp_get_dpcd(intel_dp)) {
+	/* Now read the DPCD to see if it's actually running
+	 * Don't return immediately if dpcd read failed,
+	 * if sink count was 1 and dpcd read failed we need
+	 * to do full detection
+	 */
+	ret = intel_dp_get_dpcd(intel_dp);
+
+	if (old_sink_count != intel_dp->sink_count)
+		*perform_full_detect = true;
The point I was trying to make earlier is that how can you trust
intel_dp->sink_count if intel_dp_get_dpcd failed? You don't know where
it failed, and ->sink_count may or may not have changed. Maybe it has
changed for real but you didn't have a chance to read it just yet.

+
+	/* No need to proceed if we are going to do full detect */
+	if (!ret || *perform_full_detect)
  		return;
-	}
So if you're returning because of !ret, *perform_full_detect may be true
or false, you don't know. I'd like the code to be explicit about what
you want the caller to do when intel_dp_get_dpcd returns false, full
detect or not.

BR,
Jani.
the idea i had in mind was if intel_dp_get_dpcd failed we should do a full detect.

my assumption here was that sink_count would be zero so it would take care
of this, but now that it seems to be a wrong assumption how about the following code ?
this makes it explicit that if dpcd read failed we will do full detect.

+	if ((old_sink_count != intel_dp->sink_count) || !ret)
+		*perform_full_detect = true;

+
+	/* No need to proceed if we are going to do full detect */
+	if (*perform_full_detect)
 		return;


if (!intel_encoder->base.crtc)
  		return;
@@ -5031,13 +5044,17 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
  		}
if (!intel_dp->is_mst) {
+			bool full_detect;
  			/*
  			 * we'll check the link status via the normal hot plug path later -
  			 * but for short hpds we should check it now
  			 */
  			drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
-			intel_dp_check_link_status(intel_dp);
+			intel_dp_check_link_status(intel_dp, &full_detect);
  			drm_modeset_unlock(&dev->mode_config.connection_mutex);
+
+			if (full_detect)
+				goto put_power;
  		}
  	}
--
1.7.9.5


--
regards,
Sivakumar

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