[Intel-gfx] [PATCH 2/9] drm/i915: Update intel_dp_check_link_status() for Displayport compliance testing

[Todd Previte]

Move the DPCD read to the top and check for an interrupt from the sink to catch
Displayport automated testing requests necessary to support Displayport
compliance testing. The checks for active connectors and link status are moved
below the check for the interrupt.

The main reason for doing this is to make sure that a test request isn't missed.
Checking for the status of the encoder/crtc isn't necessary for some test cases
(AUX channel tests are one example) and without moving the check for the
interrupt, these tests may not execute if one of those checks fails.
Additionally, if reading the DPCD fails, regardless of whether or not testing is
happening, there's no way to train the link since configurations and status
can't be read, nor can link training parameters be written.

Adds a check at the top to verify that the device is connected. This is
necessary for DP compliance testing to ensure that test requests are captured
and acknowledged. If a test request is present during a connected->disconnected
transition, the test code will attempt to execute even though the connection has
been disabled, resulting in a faied test.

This patch is actually both a bug fix and a component of compliance testing.
Because HPD events are received both on connect and disconnect actions, it's
vital that we don't try and train the link when we're transitioning from
connected->disconnected. That results in errors and warning in the logs from
failed AUX transactions and can trigger the WARN for the check of !base.crtc.
By making the check at the beginning to see if the connection is truly active,
those problems are avoided and testing / link training will only be attempted
when there is a valid Displayport connection.

V2:
- N/A
V3:
- Removed extraneous comment
- Added responses to review feedback into the patch notes

Signed-off-by: Todd Previte <tprevite at gmail.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 25ffa7d..280ae7a 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -3887,21 +3887,13 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
 
 	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
 
-	if (!intel_encoder->connectors_active)
-		return;
-
-	if (WARN_ON(!intel_encoder->base.crtc))
-		return;
-
-	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
-		return;
-
-	/* Try to read receiver status if the link appears to be up */
-	if (!intel_dp_get_link_status(intel_dp, link_status)) {
+	if (intel_dp->attached_connector->base.status !=
+	    connector_status_connected) {
+		DRM_DEBUG_KMS("Not connected\n");
 		return;
 	}
 
-	/* Now read the DPCD to see if it's actually running */
+	/* Attempt to read the DPCD */
 	if (!intel_dp_get_dpcd(intel_dp)) {
 		return;
 	}
@@ -3913,13 +3905,26 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
 		drm_dp_dpcd_writeb(&intel_dp->aux,
 				   DP_DEVICE_SERVICE_IRQ_VECTOR,
 				   sink_irq_vector);
-
 		if (sink_irq_vector & DP_AUTOMATED_TEST_REQUEST)
 			intel_dp_handle_test_request(intel_dp);
 		if (sink_irq_vector & (DP_CP_IRQ | DP_SINK_SPECIFIC_IRQ))
 			DRM_DEBUG_DRIVER("CP or sink specific irq unhandled\n");
 	}
 
+	if (!intel_encoder->connectors_active)
+		return;
+
+	if (WARN_ON(!intel_encoder->base.crtc))
+		return;
+
+	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
+		return;
+
+	/* Try to read receiver status if the link appears to be up */
+	if (!intel_dp_get_link_status(intel_dp, link_status)) {
+		return;
+	}
+
 	if (!drm_dp_channel_eq_ok(link_status, intel_dp->lane_count)) {
 		DRM_DEBUG_KMS("%s: channel EQ not ok, retraining\n",
 			      intel_encoder->base.name);
-- 
1.9.1