[PATCH 3/4] drm/i915: dp: Reset link params in compute_config if necessary

[Sean Paul]

From: Sean Paul <seanpaul at chromium.org>

Currently compute_config() will continue without ensuring the link
parameters are correct. If the dpcd information is invalid, this will
result in a bogus config. So either reset the link parameters if dpcd is
valid, or fail compute_config() if they're not.

Cc: stable at vger.kernel.org
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Sean Paul <seanpaul at chromium.org>
---
 drivers/gpu/drm/i915/intel_dp.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index fcce82509044..aba89baaa7f6 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -2066,6 +2066,11 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
 	return true;
 }
 
+static bool intel_dp_dpcd_valid(struct intel_dp *intel_dp)
+{
+	return intel_dp->dpcd[DP_DPCD_REV] != 0;
+}
+
 static void
 intel_dp_reset_link_params(struct intel_dp *intel_dp)
 {
@@ -2098,6 +2103,19 @@ intel_dp_compute_config(struct intel_encoder *encoder,
 	bool constant_n = drm_dp_has_quirk(&intel_dp->desc,
 					   DP_DPCD_QUIRK_CONSTANT_N);
 
+	/*
+	 * Can't compute the config if the link parameters are invalid. This
+	 * case can be hit on resume where we assume the same display is
+	 * connected and go straight to a modeset. If we have valid dpcd info,
+	 * reset the link parameters, otherwise fail out.
+	 */
+	if (intel_dp->reset_link_params) {
+		if (intel_dp_dpcd_valid(intel_dp))
+			intel_dp_reset_link_params(intel_dp);
+		else
+			return false;
+	}
+
 	if (HAS_PCH_SPLIT(dev_priv) && !HAS_DDI(dev_priv) && port != PORT_A)
 		pipe_config->has_pch_encoder = true;
 
@@ -3968,7 +3986,7 @@ intel_dp_read_dpcd(struct intel_dp *intel_dp)
 
 	DRM_DEBUG_KMS("DPCD: %*ph\n", (int) sizeof(intel_dp->dpcd), intel_dp->dpcd);
 
-	return intel_dp->dpcd[DP_DPCD_REV] != 0;
+	return intel_dp_dpcd_valid(intel_dp);
 }
 
 static bool
-- 
Sean Paul, Software Engineer, Google / Chromium OS