leds: wago-m4: eliminate boot delay by polling rproc with short interval

The previous approach tried to peek at the rproc state in probe() to
decide whether to use delay=0 (SPL path) or 5000ms (Linux-boot path).
This did not work because the remoteproc subsystem registers the rproc
device ~140ms after the LED driver probes, so rproc_get_by_phandle()
always returned NULL at probe() time and the 5000ms delay was always
used.

New approach:
- Schedule boot_work with delay=0 unconditionally from probe().
- Reduce WAGO_BOOT_RETRY_MS from 2000ms to 200ms so the rproc handle
  is found within one retry after it becomes available (~200ms total).
- Increase WAGO_BOOT_MAX_RETRIES from 30 to 150 to keep the same
  total worst-case timeout (150 x 200ms = 30s for rproc polling).
- For the Linux-boot path (-ENOENT, firmware file not found), switch
  directly to WAGO_BOOT_INITIAL_DELAY_MS (5000ms) per retry instead
  of the short rproc-poll interval to avoid hammering the filesystem.

Expected boot timeline (SPL path):
  [0.797] probe()          -> boot_work scheduled, delay=0
  [0.797] boot_work #1     -> rproc not yet available, retry in 200ms
  [0.997] boot_work #2     -> rproc DETACHED, attach immediately
  [~1.0 ] RPMsg channel up -> LED strip active

Signed-off-by: Heinrich Toews <ht@twx-software.de>

drivers/leds/rgb/wago-m4-led-wrapper.c

@@ -108,12 +108,14 @@
 /* Maximum ASCII command length for sysfs passthrough */
 #define WAGO_CMD_MAX_LEN	32
 
-/* First boot attempt this many ms after probe() */
+/* First boot attempt this many ms after probe() — Linux-boot path only,
+ * gives the rootfs time to mount before loading firmware from /lib/firmware.
+ * Not used in the SPL path (M4 already running). */
 #define WAGO_BOOT_INITIAL_DELAY_MS	5000
-/* Retry interval when filesystem is not yet available */
-#define WAGO_BOOT_RETRY_MS		2000
+/* Retry interval when rproc is not yet registered or firmware not found */
+#define WAGO_BOOT_RETRY_MS		200
 /* Maximum number of boot attempts before giving up */
-#define WAGO_BOOT_MAX_RETRIES		30
+#define WAGO_BOOT_MAX_RETRIES		150
 
 /*
  * vring TX ring retry policy for rpmsg_trysend().
@@ -716,12 +718,14 @@ static void wago_boot_work(struct work_struct *work)
 
 	/*
 	 * -ENOENT: firmware file not found — rootfs not yet mounted.
-	 * Retry after a short delay.
+	 * Switch to the longer retry interval for filesystem polling.
 	 */
 	if (ret == -ENOENT) {
 		dev_dbg(dev, "Firmware not found yet, retrying in %d ms\n",
-			WAGO_BOOT_RETRY_MS);
-		goto retry;
+			WAGO_BOOT_INITIAL_DELAY_MS);
+		schedule_delayed_work(&priv->boot_work,
+				      msecs_to_jiffies(WAGO_BOOT_INITIAL_DELAY_MS));
+		return;
 	}
 
 	dev_err(dev, "rproc_boot failed: %d\n", ret);
@@ -768,9 +772,7 @@ static void wago_rproc_stop(struct wago_m4_led_priv *priv)
 static int wago_m4_led_probe(struct platform_device *pdev)
 {
 	struct wago_m4_led_priv *priv;
-	struct device_node *rproc_np;
 	const char *fw_name;
-	unsigned long boot_delay_ms;
 	int ret;
 
 	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
@@ -822,41 +824,21 @@ static int wago_m4_led_probe(struct platform_device *pdev)
 #endif /* CONFIG_LEDS_WAGO_M4_WRAPPER_SYSFS_PASSTHROUGH */
 
 	/*
-	 * Determine boot delay:
+	 * Schedule boot_work immediately (delay=0).
 	 *
-	 * If the rproc is already available and in RPROC_DETACHED state
-	 * (U-Boot / SPL loaded the firmware), schedule boot_work immediately
-	 * so the RPMsg channel comes up as fast as possible.
-	 *
-	 * Otherwise use WAGO_BOOT_INITIAL_DELAY_MS to give the rootfs time
-	 * to mount before we try to load the firmware file.
+	 * boot_work polls for the rproc handle with WAGO_BOOT_RETRY_MS
+	 * intervals (200 ms). Once the rproc is registered by the remoteproc
+	 * subsystem it checks the state:
+	 *   RPROC_DETACHED -> attach right away (SPL path, ~1 retry needed)
+	 *   otherwise      -> load firmware from /lib/firmware (Linux-boot path,
+	 *                     retries until rootfs is mounted)
 	 */
-	boot_delay_ms = WAGO_BOOT_INITIAL_DELAY_MS;
-	rproc_np = of_parse_phandle(pdev->dev.of_node, "remoteproc", 0);
-	if (rproc_np) {
-		struct rproc *rp = rproc_get_by_phandle(rproc_np->phandle);
-
-		of_node_put(rproc_np);
-		if (!IS_ERR_OR_NULL(rp)) {
-			if (rp->state == RPROC_DETACHED) {
-				boot_delay_ms = 0;
-				dev_info(&pdev->dev,
-					 "M4 already running (SPL path), "
-					 "attaching immediately\n");
-			}
-			/* rproc_boot_work will re-acquire it lazily */
-			rproc_put(rp);
-		}
-	}
-
 	INIT_DELAYED_WORK(&priv->boot_work, wago_boot_work);
-	schedule_delayed_work(&priv->boot_work,
-			      msecs_to_jiffies(boot_delay_ms));
+	schedule_delayed_work(&priv->boot_work, 0);
 
 	dev_info(&pdev->dev,
-		 "WAGO M4 LED wrapper probed, %d LEDs active, "
-		 "RPMsg attach in %lu ms\n",
-		 WAGO_LED_NUM_LEDS, boot_delay_ms);
+		 "WAGO M4 LED wrapper probed, %d LEDs active\n",
+		 WAGO_LED_NUM_LEDS);
 	return 0;
 }