[PATCH 11/17] drm/i915: Update the EDID automated compliance test function

[Todd Previte <tprevite@gmail.com>]

Updates the EDID compliance test function to perform the EDID read as
required by the tests. This read needs to take place in the kernel for
reasons of speed and efficiency. The results of the EDID read are handed
off to userspace so that the remainder of the test can be conducted there.

V2:
- Addressed mailing list feedback
- Removed excess debug messages
- Removed extraneous comments
- Fixed formatting issues (line length > 80)
- Updated the debug message in compute_edid_checksum to output hex values
  instead of decimal

Signed-off-by: Todd Previte <tprevite@gmail.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 72 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 71 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index b6f5a72..2a13124 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -40,6 +40,13 @@
 
 #define DP_LINK_CHECK_TIMEOUT	(10 * 1000)
 
+/* Compliance test status bits  */
+#define  INTEL_DP_EDID_OK		(0<<0)
+#define  INTEL_DP_EDID_CORRUPT		(1<<0)
+#define  INTEL_DP_RESOLUTION_PREFERRED	(1<<2)
+#define  INTEL_DP_RESOLUTION_STANDARD	(1<<3)
+#define  INTEL_DP_RESOLUTION_FAILSAFE	(1<<4)
+
 struct dp_link_dpll {
 	int link_bw;
 	struct dpll dpll;
@@ -3761,9 +3768,72 @@ static uint8_t intel_dp_autotest_video_pattern(struct intel_dp *intel_dp)
 	return test_result;
 }
 
+static bool intel_dp_compute_edid_checksum(uint8_t *edid_data,
+					   uint8_t *edid_checksum)
+{
+	uint32_t byte_total = 0;
+	uint8_t i = 0;
+	bool edid_ok = true;
+
+	/* Don't include last byte (the checksum) in the computation */
+	for (i = 0; i < EDID_LENGTH - 2; i++)
+		byte_total += edid_data[i];
+
+	*edid_checksum = 256 - (byte_total % 256);
+
+	if (*edid_checksum != edid_data[EDID_LENGTH - 1]) {
+		DRM_DEBUG_KMS("Invalid EDID checksum %02x, should be %02x\n",
+			      edid_data[EDID_LENGTH - 40 - 1], *edid_checksum);
+		edid_ok = false;
+	}
+
+	return edid_ok;
+}
+
 static uint8_t intel_dp_autotest_edid(struct intel_dp *intel_dp)
 {
-	uint8_t test_result = DP_TEST_NAK;
+	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, checksum = 0;
+	uint32_t ret = 0;
+
+	intel_dp->aux.i2c_nack_count = 0;
+	intel_dp->aux.i2c_defer_count = 0;
+
+	edid_read = drm_get_edid(connector, adapter);
+
+	if (edid_read == NULL) {
+		/* Check for NACKs/DEFERs, use failsafe if detected
+		   (DP CTS 1.2 Core Rev 1.1, 4.2.2.4, 4.2.2.5) */
+		if (intel_dp->aux.i2c_nack_count > 0 ||
+			intel_dp->aux.i2c_defer_count > 0)
+			DRM_DEBUG_KMS("EDID read had %d NACKs, %d DEFERs\n",
+				      intel_dp->aux.i2c_nack_count,
+				      intel_dp->aux.i2c_defer_count);
+		intel_dp->compliance_test_data = INTEL_DP_EDID_CORRUPT |
+						 INTEL_DP_RESOLUTION_FAILSAFE;
+	} else {
+		edid_data = (uint8_t *) edid_read;
+
+		if (intel_dp_compute_edid_checksum(edid_data, &checksum)) {
+			ret = drm_dp_dpcd_write(&intel_dp->aux,
+						DP_TEST_EDID_CHECKSUM,
+						&edid_read->checksum, 1);
+			test_result = DP_TEST_ACK |
+				      DP_TEST_EDID_CHECKSUM_WRITE;
+			intel_dp->compliance_test_data =
+				INTEL_DP_EDID_OK |
+				INTEL_DP_RESOLUTION_PREFERRED;
+		} else {
+			/* Invalid checksum - EDID corruption detection */
+			intel_dp->compliance_test_data =
+				INTEL_DP_EDID_CORRUPT |
+				INTEL_DP_RESOLUTION_FAILSAFE;
+		}
+	}
+
 	return test_result;
 }
 
-- 
1.9.1

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