[PATCH 3/6] drm/i915: Implement basic Displayport automated testing function for EDID operations

[Todd Previte <tprevite@gmail.com>]

Implements some of the basic EDID tests for Displayport compliance. These tests
include reading the EDID, verifying the checksum and writing the test responses
back to the sink device.

Signed-off-by: Todd Previte <tprevite@gmail.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 43fcabe..d060853 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -3352,8 +3352,42 @@ intel_dp_autotest_video_pattern(struct intel_dp *intel_dp)
 static uint8_t
 intel_dp_autotest_edid(struct intel_dp *intel_dp)
 {
+	struct drm_connector *connector = &intel_dp->attached_connector->base;
+	struct i2c_adapter *adapter = &intel_dp->aux.ddc;
+	struct edid *edid_read = NULL;
+	uint8_t *edid_data = NULL;
 	uint8_t test_result = DP_TEST_NAK;
-	return test_result;
+	uint32_t i = 0, ret = 0, checksum = 0;
+	struct drm_display_mode *use_mode = NULL;
+	dp_compliance_mode comp_mode_type = DP_COMPLIANCE_MODE_PREFERRED;
+	int mode_count = 0;
+
+	edid_read = drm_get_edid(connector, adapter);
+
+	DRM_DEBUG_KMS("Displayport: EDID automated test\n");
+
+	if (edid_read) {
+		test_result = true;
+		edid_data = (uint8_t*) edid_read;
+		// Compute checksum
+		for (i = 0; i < 128; i++)
+				checksum += edid_data[i];
+
+		DRM_DEBUG_KMS("Displayport: EDID test - computed byte sum = %02x\n", checksum);
+		// Verify EDID checksum
+		if (checksum % 256 == 0) {
+			/* Write the checksum to EDID checksum register */
+			ret = drm_dp_dpcd_write(&intel_dp->aux, DP_TEST_EDID_CHECKSUM, &edid_read->checksum, 1);
+			// Reponse is ACK and and checksum written
+			test_result = DP_TEST_ACK | DP_TEST_EDID_CHECKSUM_WRITE;
+			DRM_DEBUG_KMS("Displayport: EDID test - checksum = %02x\n", edid_read->checksum);
+		}
+		else {
+			// Invalid checksum, set for failsafe mode
+			comp_mode_type = DP_COMPLIANCE_MODE_FAILSAFE;
+		}
+	}
+        return test_result;
 }
 
 /* Displayport compliance testing - PHY pattern testing */
-- 
1.9.1