drm/bridge: it6505: fix HDCP CTS compare V matching

When HDCP negotiation with a repeater device.
Checking SHA V' matching must retry 3 times before restarting HDCP.

Signed-off-by: Hermes Wu <[email protected]>
Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
Signed-off-by: Dmitry Baryshkov <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/20241230-v7-upstream-v7-8-e0fdd4844703@ite.corp-partner.google.com

Author: Hermes Wu

drivers/gpu/drm/bridge/ite-it6505.c

@@ -2058,7 +2058,7 @@ static bool it6505_hdcp_part2_ksvlist_check(struct it6505 *it6505)
 {
 	struct device *dev = it6505->dev;
 	u8 av[5][4], bv[5][4];
-	int i, err;
+	int i, err, retry;
 
 	i = it6505_setup_sha1_input(it6505, it6505->sha1_input);
 	if (i <= 0) {
@@ -2067,22 +2067,28 @@ static bool it6505_hdcp_part2_ksvlist_check(struct it6505 *it6505)
 	}
 
 	it6505_sha1_digest(it6505, it6505->sha1_input, i, (u8 *)av);
+	/*1B-05 V' must retry 3 times */
+	for (retry = 0; retry < 3; retry++) {
+		err = it6505_get_dpcd(it6505, DP_AUX_HDCP_V_PRIME(0), (u8 *)bv,
+				      sizeof(bv));
 
-	err = it6505_get_dpcd(it6505, DP_AUX_HDCP_V_PRIME(0), (u8 *)bv,
-			      sizeof(bv));
+		if (err < 0) {
+			dev_err(dev, "Read V' value Fail %d", retry);
+			continue;
+		}
 
-	if (err < 0) {
-		dev_err(dev, "Read V' value Fail");
-		return false;
-	}
+		for (i = 0; i < 5; i++) {
+			if (bv[i][3] != av[i][0] || bv[i][2] != av[i][1] ||
+			    av[i][1] != av[i][2] || bv[i][0] != av[i][3])
+				break;
 
-	for (i = 0; i < 5; i++)
-		if (bv[i][3] != av[i][0] || bv[i][2] != av[i][1] ||
-		    bv[i][1] != av[i][2] || bv[i][0] != av[i][3])
-			return false;
+			DRM_DEV_DEBUG_DRIVER(dev, "V' all match!! %d, %d", retry, i);
+			return true;
+		}
+	}
 
-	DRM_DEV_DEBUG_DRIVER(dev, "V' all match!!");
-	return true;
+	DRM_DEV_DEBUG_DRIVER(dev, "V' NOT match!! %d", retry);
+	return false;
 }
 
 static void it6505_hdcp_wait_ksv_list(struct work_struct *work)