[PATCH v4] drm: Add support for DP 1.4 Compliance edid corruption test 4.2.2.6

[Jerry (Fangzhi) Zuo]

DP 1.4 edid corruption test requires source DUT to write calculated
CRC, not the corrupted CRC from reference sink.

Return the calculated CRC back, and initiate the required sequence.

-v2: Have separate routine for returning real CRC

-v3: Rewrite checksum computation routine to avoid duplicated code.
     Rename to avoid confusion

-v4: Fix a minor typo.

Signed-off-by: Jerry (Fangzhi) Zuo <Jerry.Zuo at amd.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 36 ++++++++++++++++++++++++++++++++++++
 drivers/gpu/drm/drm_edid.c      | 18 +++++++++++++++---
 include/drm/drm_connector.h     |  7 +++++++
 include/drm/drm_dp_helper.h     |  3 +++
 4 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index ffc68d305afe..22a0e966ea9f 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -336,6 +336,42 @@ int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
 }
 EXPORT_SYMBOL(drm_dp_dpcd_read_link_status);
 
+/**
+  * drm_dp_send_real_edid_checksum() - send back real edid checksum value
+  * @aux: DisplayPort AUX channel
+  * @real_edid_checksum: real edid checksum for the last block
+  *
+  * Returns true on success
+  */
+bool drm_dp_send_real_edid_checksum(struct drm_dp_aux *aux,
+                                u8 real_edid_checksum)
+{
+        u8 link_edid_read = 0, auto_test_req = 0;
+        u8 test_resp = 0;
+
+        drm_dp_dpcd_read(aux, DP_DEVICE_SERVICE_IRQ_VECTOR, &auto_test_req, 1);
+        auto_test_req &= DP_AUTOMATED_TEST_REQUEST;
+
+        drm_dp_dpcd_read(aux, DP_TEST_REQUEST, &link_edid_read, 1);
+        link_edid_read &= DP_TEST_LINK_EDID_READ;
+
+        if (!auto_test_req || !link_edid_read) {
+                DRM_DEBUG_KMS("Source DUT does not support TEST_EDID_READ\n");
+                return false;
+        }
+
+        drm_dp_dpcd_write(aux, DP_DEVICE_SERVICE_IRQ_VECTOR, &auto_test_req, 1);
+
+        /* send back checksum for the last edid extension block data */
+        drm_dp_dpcd_write(aux, DP_TEST_EDID_CHECKSUM, &real_edid_checksum, 1);
+
+        test_resp |= DP_TEST_EDID_CHECKSUM_WRITE;
+        drm_dp_dpcd_write(aux, DP_TEST_RESPONSE, &test_resp, 1);
+
+        return true;
+}
+EXPORT_SYMBOL(drm_dp_send_real_edid_checksum);
+
 /**
  * drm_dp_link_probe() - probe a DisplayPort link for capabilities
  * @aux: DisplayPort AUX channel
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 82a4ceed3fcf..ff64e5f1feb6 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -1348,10 +1348,19 @@ static int drm_edid_block_checksum(const u8 *raw_edid)
 {
 	int i;
 	u8 csum = 0;
-	for (i = 0; i < EDID_LENGTH; i++)
+
+	for (i = 0; i < EDID_LENGTH - 1; i++)
 		csum += raw_edid[i];
 
-	return csum;
+	return (0x100 - csum);
+}
+
+static bool drm_edid_block_checksum_diff(const u8 *raw_edid, u8 real_checksum)
+{
+	if (raw_edid[EDID_LENGTH - 1] != real_checksum)
+		return true;
+	else
+		return false;
 }
 
 static bool drm_edid_is_zero(const u8 *in_edid, int length)
@@ -1409,7 +1418,7 @@ bool drm_edid_block_valid(u8 *raw_edid, int block, bool print_bad_edid,
 	}
 
 	csum = drm_edid_block_checksum(raw_edid);
-	if (csum) {
+	if (drm_edid_block_checksum_diff(raw_edid, csum)) {
 		if (edid_corrupt)
 			*edid_corrupt = true;
 
@@ -1572,6 +1581,9 @@ static void connector_bad_edid(struct drm_connector *connector,
 			       prefix, DUMP_PREFIX_NONE, 16, 1,
 			       block, EDID_LENGTH, false);
 	}
+
+	/* Calculate real checksum for the last edid extension block data */
+	connector->real_edid_checksum = drm_edid_block_checksum(edid + edid[0x7e] * EDID_LENGTH);
 }
 
 /* Get override or firmware EDID */
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 681cb590f952..eb0d8c7b35fd 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -1345,6 +1345,13 @@ struct drm_connector {
 	 * rev1.1 4.2.2.6
 	 */
 	bool edid_corrupt;
+	/**
+         * @real_edid_checksum: real edid checksum value for corrupted edid block.
+         * Required in Displayport 1.4 compliance testing
+         * rev1.1 4.2.2.6
+         */
+        uint8_t real_edid_checksum;
+
 
 	/** @debugfs_entry: debugfs directory for this connector */
 	struct dentry *debugfs_entry;
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 5a795075d5da..84709d7810f8 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -1383,6 +1383,9 @@ static inline ssize_t drm_dp_dpcd_writeb(struct drm_dp_aux *aux,
 int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
 				 u8 status[DP_LINK_STATUS_SIZE]);
 
+bool drm_dp_send_real_edid_checksum(struct drm_dp_aux *aux,
+				    u8 real_edid_checksum);
+
 /*
  * DisplayPort link
  */
-- 
2.14.1