linux-kernel - [RFC PATCH 1/2] backlight: Rename duplicated devices to support dual-backlight setups

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Message-ID: <20250525104022.1326997-1-mitltlatltl@gmail.com>
Date: Sun, 25 May 2025 18:40:21 +0800
From: Pengyu Luo <mitltlatltl@...il.com>
To: Lee Jones <lee@...nel.org>,
	Daniel Thompson <danielt@...nel.org>,
	Jingoo Han <jingoohan1@...il.com>,
	Helge Deller <deller@....de>
Cc: dri-devel@...ts.freedesktop.org,
	linux-fbdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Pengyu Luo <mitltlatltl@...il.com>
Subject: [RFC PATCH 1/2] backlight: Rename duplicated devices to support dual-backlight setups

When registering a backlight device, if a device with the same name
already exists, append "-secondary" to the new device's name. This is
useful for platforms with dual backlight drivers (e.g. some panels use
dual ktz8866), where both instances need to coexist.

For now, only one secondary instance is supported. If more instances
are needed, this logic can be extended with auto-increment or a more
flexible naming scheme.

Suggested-by: Daniel Thompson <danielt@...nel.org>
Signed-off-by: Pengyu Luo <mitltlatltl@...il.com>
---
 drivers/video/backlight/backlight.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index 9dc93c5e4..991702f5d 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -365,7 +365,8 @@ struct backlight_device *backlight_device_register(const char *name,
 	struct device *parent, void *devdata, const struct backlight_ops *ops,
 	const struct backlight_properties *props)
 {
-	struct backlight_device *new_bd;
+	struct backlight_device *new_bd, *prev_bd;
+	const char *new_name = NULL;
 	int rc;
 
 	pr_debug("backlight_device_register: name=%s\n", name);
@@ -377,10 +378,23 @@ struct backlight_device *backlight_device_register(const char *name,
 	mutex_init(&new_bd->update_lock);
 	mutex_init(&new_bd->ops_lock);
 
+	/*
+	 * If there is an instance with the same name already, then rename it.
+	 * We also can use an auto-increment field, but it seems that there is
+	 * no triple or quad case.
+	 */
+	prev_bd = backlight_device_get_by_name(name);
+	if (!IS_ERR_OR_NULL(prev_bd)) {
+		new_name = kasprintf(GFP_KERNEL, "%s-secondary", name);
+		if (!new_name)
+			return ERR_PTR(-ENOMEM);
+		put_device(&prev_bd->dev);
+	}
+
 	new_bd->dev.class = &backlight_class;
 	new_bd->dev.parent = parent;
 	new_bd->dev.release = bl_device_release;
-	dev_set_name(&new_bd->dev, "%s", name);
+	dev_set_name(&new_bd->dev, "%s", new_name ? new_name : name);
 	dev_set_drvdata(&new_bd->dev, devdata);
 
 	/* Set default properties */
@@ -414,6 +428,8 @@ struct backlight_device *backlight_device_register(const char *name,
 	list_add(&new_bd->entry, &backlight_dev_list);
 	mutex_unlock(&backlight_dev_list_mutex);
 
+	kfree(new_name);
+
 	return new_bd;
 }
 EXPORT_SYMBOL(backlight_device_register);
-- 
2.49.0