backlight: Match backlight device against struct fb_info.bl_dev

Framebuffer drivers for devices with dedicated backlight are supposed
to set struct fb_info.bl_dev to the backlight's respective device. Use
the value to match backlight and framebuffer in the backlight core code.

The code first tests against struct backlight_ops.check_ops. If this
test succeeds, it performs the test against fbdev. So backlight drivers
can override the later test as before.

Fbdev's backlight support depends on CONFIG_FB_BACKLIGHT. To avoid
ifdef in the code, the new helper fb_bl_device() returns the backlight
device, or NULL if the config option has been disabled. The test in
the backlight code will then do nothing.

v4:
	* declare empty fb_bl_device() as static inline
	* export fb_bl_device()
v3:
	* hide ifdef in fb_bl_device() (Lee)
	* no if-else blocks (Andy)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://lore.kernel.org/r/20240305162425.23845-2-tzimmermann@suse.de
Signed-off-by: Lee Jones <lee@kernel.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/video/fbdev/core/fb_backlight.c b/drivers/video/fbdev/core/fb_backlight.c
index e2d3b3adc870..6fdaa9f81be9 100644
--- a/drivers/video/fbdev/core/fb_backlight.c
+++ b/drivers/video/fbdev/core/fb_backlight.c
@@ -30,4 +30,10 @@ void fb_bl_default_curve(struct fb_info *fb_info, u8 off, u8 min, u8 max)
 	mutex_unlock(&fb_info->bl_curve_mutex);
 }
 EXPORT_SYMBOL_GPL(fb_bl_default_curve);
+
+struct backlight_device *fb_bl_device(struct fb_info *info)
+{
+	return info->bl_dev;
+}
+EXPORT_SYMBOL(fb_bl_device);
 #endif