drm/dp: extract drm_dp_dpcd_poll_act_handled()

SST with 128b/132b channel coding needs this too. Extract to a separate
helper, independent of MST.

Pass timeout in as a parameter, anticipating that we can reduce the
timeout for SST.

v2: Clean up kernel-doc a bit

Cc: Lyude Paul <lyude@redhat.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/459fd3e96a55a8ea8ada8d27d93eaa24c235f9c1.1733238941.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/display/drm_dp_helper.c

@@ -22,15 +22,16 @@
 
 #include <linux/backlight.h>
 #include <linux/delay.h>
+#include <linux/dynamic_debug.h>
 #include <linux/errno.h>
 #include <linux/i2c.h>
 #include <linux/init.h>
+#include <linux/iopoll.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <linux/seq_file.h>
 #include <linux/string_helpers.h>
-#include <linux/dynamic_debug.h>
 
 #include <drm/display/drm_dp_helper.h>
 #include <drm/display/drm_dp_mst_helper.h>
@@ -779,6 +780,57 @@ int drm_dp_dpcd_read_phy_link_status(struct drm_dp_aux *aux,
 }
 EXPORT_SYMBOL(drm_dp_dpcd_read_phy_link_status);
 
+static int read_payload_update_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_dpcd_poll_act_handled() - Poll for ACT handled status
+ * @aux: DisplayPort AUX channel
+ * @timeout_ms: Timeout in ms
+ *
+ * Try waiting for the sink to finish updating its payload table by polling for
+ * the ACT handled bit of DP_PAYLOAD_TABLE_UPDATE_STATUS for up to @timeout_ms
+ * milliseconds, defaulting to 3000 ms if 0.
+ *
+ * Returns:
+ * 0 if the ACT was handled in time, negative error code on failure.
+ */
+int drm_dp_dpcd_poll_act_handled(struct drm_dp_aux *aux, int timeout_ms)
+{
+	int ret, status;
+
+	/* default to 3 seconds, this is arbitrary */
+	timeout_ms = timeout_ms ?: 3000;
+
+	ret = readx_poll_timeout(read_payload_update_status, aux, status,
+				 status & DP_PAYLOAD_ACT_HANDLED || status < 0,
+				 200, timeout_ms * USEC_PER_MSEC);
+	if (ret < 0 && status >= 0) {
+		drm_err(aux->drm_dev, "Failed to get ACT after %d ms, last status: %02x\n",
+			timeout_ms, status);
+		return -EINVAL;
+	} else if (status < 0) {
+		/*
+		 * Failure here isn't unexpected - the hub may have
+		 * just been unplugged
+		 */
+		drm_dbg_kms(aux->drm_dev, "Failed to read payload table status: %d\n", status);
+		return status;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_dpcd_poll_act_handled);
+
 static bool is_edid_digital_input_dp(const struct drm_edid *drm_edid)
 {
 	/* FIXME: get rid of drm_edid_raw() */

drivers/gpu/drm/display/drm_dp_mst_topology.c

@@ -29,7 +29,6 @@
 #include <linux/random.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>
@@ -4723,18 +4722,6 @@ static int drm_dp_dpcd_write_payload(struct drm_dp_mst_topology_mgr *mgr,
 	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
@@ -4752,28 +4739,9 @@ int drm_dp_check_act_status(struct drm_dp_mst_topology_mgr *mgr)
 	 * 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.
+	 * conditions, we use a rather large timeout value of 3 seconds.
 	 */
-	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_err(mgr->dev, "Failed to get ACT after %dms, last status: %02x\n",
-			timeout_ms, status);
-		return -EINVAL;
-	} else if (status < 0) {
-		/*
-		 * Failure here isn't unexpected - the hub may have
-		 * just been unplugged
-		 */
-		drm_dbg_kms(mgr->dev, "Failed to read payload table status: %d\n", status);
-		return status;
-	}
-
-	return 0;
+	return drm_dp_dpcd_poll_act_handled(mgr->aux, 3000);
 }
 EXPORT_SYMBOL(drm_dp_check_act_status);
 

include/drm/display/drm_dp_helper.h

@@ -567,6 +567,8 @@ int drm_dp_dpcd_read_phy_link_status(struct drm_dp_aux *aux,
 				     enum drm_dp_phy dp_phy,
 				     u8 link_status[DP_LINK_STATUS_SIZE]);
 
+int drm_dp_dpcd_poll_act_handled(struct drm_dp_aux *aux, int timeout_ms);
+
 bool drm_dp_send_real_edid_checksum(struct drm_dp_aux *aux,
 				    u8 real_edid_checksum);