[PATCH 4/9] drm/i915: Add check for corrupt raw EDID header for Displayport compliance testing

[Todd Previte]

Displayport compliance test 4.2.2.6 requires that a source device be capable of detecting
a corrupt EDID. To do this, the test sets up an invalid EDID header to be read by the source
device. Unfortunately, the DRM EDID reading and parsing functions are actually too good in
this case and prevent the source from reading the corrupted EDID. The result is a failed
compliance test.

In order to successfully pass the test, the raw EDID header must be checked on each read
to see if has been "corrupted". If an invalid raw header is detected, a flag is set that
allows the compliance testing code to acknowledge that fact and react appropriately. The
flag is automatically cleared on read.

This code is designed to expressly work for compliance testing without disrupting normal
operations for EDID reading and parsing.

Signed-off-by: Todd Previte <tprevite at gmail.com>
Cc: dri-devel at lists.freedesktop.org
---
 drivers/gpu/drm/drm_edid.c       | 33 +++++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_dp.c  | 17 +++++++++++++++++
 drivers/gpu/drm/i915/intel_drv.h |  1 +
 include/drm/drm_edid.h           |  5 +++++
 4 files changed, 56 insertions(+)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 53bc7a6..3d4f473 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -990,6 +990,32 @@ static const u8 edid_header[] = {
 	0x00, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x00
 };
 
+
+/* Flag for EDID corruption testing
+ * Displayport Link CTS Core 1.2 rev1.1 - 4.2.2.6
+ */
+static bool raw_edid_header_corrupted;
+
+/**
+ * drm_raw_edid_header_valid - check to see if the raw header is
+ * corrupt or not. Used solely for Displayport compliance
+ * testing and required by Link CTS Core 1.2 rev1.1 4.2.2.6.
+ * @raw_edid: pointer to raw base EDID block
+ *
+ * Indicates whether the original EDID header as read from the
+ * device was corrupt or not. Clears on read.
+ *
+ * Return: true if the raw header was corrupt, otherwise false
+ */
+bool drm_raw_edid_header_corrupt(void)
+{
+	bool corrupted = raw_edid_header_corrupted;
+
+	raw_edid_header_corrupted = 0;
+	return corrupted;
+}
+EXPORT_SYMBOL(drm_raw_edid_header_corrupt);
+
 /**
  * drm_edid_header_is_valid - sanity check the header of the base EDID block
  * @raw_edid: pointer to raw base EDID block
@@ -1006,6 +1032,13 @@ int drm_edid_header_is_valid(const u8 *raw_edid)
 		if (raw_edid[i] == edid_header[i])
 			score++;
 
+	if (score != 8) {
+		/* Log and set flag here for EDID corruption testing
+		 * Displayport Link CTS Core 1.2 rev1.1 - 4.2.2.6
+		 */
+		DRM_DEBUG_DRIVER("Raw EDID header invalid\n");
+		raw_edid_header_corrupted = 1;
+	}
 	return score;
 }
 EXPORT_SYMBOL(drm_edid_header_is_valid);
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index dc87276..57f8e43 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -3824,6 +3824,9 @@ update_status:
 				   &response, 1);
 	if (status <= 0)
 		DRM_DEBUG_KMS("Could not write test response to sink\n");
+
+	/* Clear flag here, after testing is complete*/
+	intel_dp->compliance_edid_invalid = 0;
 }
 
 static int
@@ -3896,6 +3899,10 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
 {
 	struct drm_device *dev = intel_dp_to_dev(intel_dp);
 	struct intel_encoder *intel_encoder = &dp_to_dig_port(intel_dp)->base;
+	struct drm_connector *connector = &intel_dp->attached_connector->base;
+	struct i2c_adapter *adapter = &intel_dp->aux.ddc;
+	struct edid *edid_read = NULL;
+
 	u8 sink_irq_vector;
 	u8 link_status[DP_LINK_STATUS_SIZE];
 
@@ -3912,6 +3919,16 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
 		return;
 	}
 
+	/* Compliance testing requires an EDID read for all HPD events
+	 * Link CTS Core 1.2 rev 1.1: Test 4.2.2.1
+	 * Flag set here will be handled in the EDID test function
+	 */
+	edid_read = drm_get_edid(connector, adapter);
+	if (!edid_read || drm_raw_edid_header_corrupt() == 1) {
+		DRM_DEBUG_DRIVER("EDID invalid, setting flag\n");
+		intel_dp->compliance_edid_invalid = 1;
+	}
+
 	/* Try to read the source of the interrupt */
 	if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11 &&
 	    intel_dp_get_sink_irq(intel_dp, &sink_irq_vector)) {
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index e7b62be..42e4251 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -651,6 +651,7 @@ struct intel_dp {
 	/* Displayport compliance testing */
 	unsigned long compliance_test_type;
 	bool compliance_testing_active;
+	bool compliance_edid_invalid;
 };
 
 struct intel_digital_port {
diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
index 87d85e8..8a7eb22 100644
--- a/include/drm/drm_edid.h
+++ b/include/drm/drm_edid.h
@@ -388,4 +388,9 @@ struct edid *drm_do_get_edid(struct drm_connector *connector,
 			      size_t len),
 	void *data);
 
+/* Check for corruption in raw EDID header - Displayport compliance
+  * Displayport Link CTS Core 1.2 rev1.1 - 4.2.2.6
+ */
+bool drm_raw_edid_header_corrupt(void);
+
 #endif /* __DRM_EDID_H__ */
-- 
1.9.1