dm: stdio: Allow lazy probing of video devices

At present all video devices are probed on start-up. It would be better to
probe a device only when it is needed. This can happen if it is referenced
in the stdout environment variable, for example.

Add support for this by searching for a suitable device when needed, probing
it, and finding the stdio device it creates.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

common/stdio.c

@@ -121,19 +121,87 @@ struct list_head* stdio_get_list(void)
 	return &(devs.list);
 }
 
+#ifdef CONFIG_DM_VIDEO
+/**
+ * stdio_probe_device() - Find a device which provides the given stdio device
+ *
+ * This looks for a device of the given uclass which provides a particular
+ * stdio device. It is currently really only useful for UCLASS_VIDEO.
+ *
+ * Ultimately we want to be able to probe a device by its stdio name. At
+ * present devices register in their probe function (for video devices this
+ * is done in vidconsole_post_probe()) and we don't know what name they will
+ * use until they do so.
+ * TODO(sjg@chromium.org): We should be able to determine the name before
+ * probing, and probe the required device.
+ *
+ * @name:	stdio device name (e.g. "vidconsole")
+ * id:		Uclass ID of device to look for (e.g. UCLASS_VIDEO)
+ * @sdevp:	Returns stdout device, if found, else NULL
+ * @return 0 if found, -ENOENT if no device found with that name, other -ve
+ *	   on other error
+ */
+static int stdio_probe_device(const char *name, enum uclass_id id,
+			      struct stdio_dev **sdevp)
+{
+	struct stdio_dev *sdev;
+	struct udevice *dev;
+	int seq, ret;
+
+	*sdevp = NULL;
+	seq = trailing_strtoln(name, NULL);
+	if (seq == -1)
+		ret = uclass_first_device_err(id, &dev);
+	else
+		ret = uclass_get_device_by_seq(id, seq, &dev);
+	if (ret) {
+		debug("No %s device for seq %d (%s)\n", uclass_get_name(id),
+		      seq, name);
+		return ret;
+	}
+	/* The device should be be the last one registered */
+	sdev = list_empty(&devs.list) ? NULL :
+			list_last_entry(&devs.list, struct stdio_dev, list);
+	if (!sdev || strcmp(sdev->name, name)) {
+		debug("Device '%s' did not register with stdio as '%s'\n",
+		      dev->name, name);
+		return -ENOENT;
+	}
+	*sdevp = sdev;
+
+	return 0;
+}
+#endif
+
 struct stdio_dev* stdio_get_by_name(const char *name)
 {
 	struct list_head *pos;
-	struct stdio_dev *dev;
+	struct stdio_dev *sdev;
 
 	if(!name)
 		return NULL;
 
 	list_for_each(pos, &(devs.list)) {
-		dev = list_entry(pos, struct stdio_dev, list);
+		sdev = list_entry(pos, struct stdio_dev, list);
-		if(strcmp(dev->name, name) == 0)
+		if (strcmp(sdev->name, name) == 0)
-			return dev;
+			return sdev;
 	}
+#ifdef CONFIG_DM_VIDEO
+	/*
+	 * We did not find a suitable stdio device. If there is a video
+	 * driver with a name starting with 'vidconsole', we can try probing
+	 * that in the hope that it will produce the required stdio device.
+	 *
+	 * This function is sometimes called with the entire value of
+	 * 'stdout', which may include a list of devices separate by commas.
+	 * Obviously this is not going to work, so we ignore that case. The
+	 * call path in that case is console_init_r() -> search_device() ->
+	 * stdio_get_by_name().
+	 */
+	if (!strncmp(name, "vidconsole", 10) && !strchr(name, ',') &&
+	    !stdio_probe_device(name, UCLASS_VIDEO, &sdev))
+		return sdev;
+#endif
 
 	return NULL;
 }
@@ -282,6 +350,16 @@ int stdio_add_devices(void)
 #endif
 #endif
 #ifdef CONFIG_DM_VIDEO
+	/*
+	 * If the console setting is not in environment variables then
+	 * console_init_r() will not be calling iomux_doenv() (which calls
+	 * search_device()). So we will not dynamically add devices by
+	 * calling stdio_probe_device().
+	 *
+	 * So just probe all video devices now so that whichever one is
+	 * required will be available.
+	 */
+#ifndef CONFIG_SYS_CONSOLE_IS_IN_ENV
 	struct udevice *vdev;
 # ifndef CONFIG_DM_KEYBOARD
 	int ret;
@@ -293,6 +371,7 @@ int stdio_add_devices(void)
 		;
 	if (ret)
 		printf("%s: Video device failed (ret=%d)\n", __func__, ret);
+#endif /* !CONFIG_SYS_CONSOLE_IS_IN_ENV */
 #else
 # if defined(CONFIG_LCD)
 	drv_lcd_init ();