1 files changed, 34 insertions, 23 deletions

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index e7a5bd3e6015..8942ab98ab64 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -27,6 +27,7 @@
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/seq_file.h>
+#include <linux/iopoll.h>
 
 #if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)
 #include <linux/stacktrace.h>
@@ -4438,43 +4439,53 @@ fail:
 	return ret;
 }
 
+static int do_get_act_status(struct drm_dp_aux *aux)
+{
+	int ret;
+	u8 status;
+
+	ret = drm_dp_dpcd_readb(aux, DP_PAYLOAD_TABLE_UPDATE_STATUS, &status);
+	if (ret < 0)
+		return ret;
+
+	return status;
+}
 
 /**
  * drm_dp_check_act_status() - Polls for ACT handled status.
  * @mgr: manager to use
  *
  * Tries waiting for the MST hub to finish updating it's payload table by
- * polling for the ACT handled bit.
+ * polling for the ACT handled bit for up to 3 seconds (yes-some hubs really
+ * take that long).
  *
  * Returns:
  * 0 if the ACT was handled in time, negative error code on failure.
  */
 int drm_dp_check_act_status(struct drm_dp_mst_topology_mgr *mgr)
 {
-	int count = 0, ret;
-	u8 status;
-
-	do {
-		ret = drm_dp_dpcd_readb(mgr->aux,
-					DP_PAYLOAD_TABLE_UPDATE_STATUS,
-					&status);
-		if (ret < 0) {
-			DRM_DEBUG_KMS("failed to read payload table status %d\n",
-				      ret);
-			return ret;
-		}
-
-		if (status & DP_PAYLOAD_ACT_HANDLED)
-			break;
-		count++;
-		udelay(100);
-	} while (count < 30);
-
-	if (!(status & DP_PAYLOAD_ACT_HANDLED)) {
-		DRM_DEBUG_KMS("failed to get ACT bit %d after %d retries\n",
-			      status, count);
+	/*
+	 * There doesn't seem to be any recommended retry count or timeout in
+	 * the MST specification. Since some hubs have been observed to take
+	 * over 1 second to update their payload allocations under certain
+	 * conditions, we use a rather large timeout value.
+	 */
+	const int timeout_ms = 3000;
+	int ret, status;
+
+	ret = readx_poll_timeout(do_get_act_status, mgr->aux, status,
+				 status & DP_PAYLOAD_ACT_HANDLED || status < 0,
+				 200, timeout_ms * USEC_PER_MSEC);
+	if (ret < 0 && status >= 0) {
+		DRM_DEBUG_KMS("Failed to get ACT after %dms, last status: %02x\n",
+			      timeout_ms, status);
 		return -EINVAL;
+	} else if (status < 0) {
+		DRM_DEBUG_KMS("Failed to read payload table status: %d\n",
+			      status);
+		return status;
 	}
+
 	return 0;
 }
 EXPORT_SYMBOL(drm_dp_check_act_status);