On Tue, Dec 10, 2024, at 15:09, Thomas Zimmermann wrote:

Do not select BACKLIGHT_CLASS_DEVICE from FB_BACKLIGHT. The latter
only controls backlight support within fbdev core code and data
structures.

Make fbdev drivers depend on BACKLIGHT_CLASS_DEVICE and let users
select it explicitly. Fixes warnings about recursive dependencies,
such as

error: recursive dependency detected!
	symbol BACKLIGHT_CLASS_DEVICE is selected by FB_BACKLIGHT
	symbol FB_BACKLIGHT is selected by FB_SH_MOBILE_LCDC
	symbol FB_SH_MOBILE_LCDC depends on FB_DEVICE
	symbol FB_DEVICE depends on FB_CORE
	symbol FB_CORE is selected by DRM_GEM_DMA_HELPER
	symbol DRM_GEM_DMA_HELPER is selected by DRM_PANEL_ILITEK_ILI9341
	symbol DRM_PANEL_ILITEK_ILI9341 depends on BACKLIGHT_CLASS_DEVICE

BACKLIGHT_CLASS_DEVICE is user-selectable, so making drivers adapt to
it is the correct approach in any case. For most drivers, backlight
support is also configurable separately.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>

Thanks for revisiting this!

My patch that failed to work correctly happened to work on my
randconfig tree because I still have an old variant of this
change, see

https://lore.kernel.org/linux-fbdev/20200417155553.675905-8-arnd@arndb.de/ (local)

This is almost the same as your version, except for the
optional fbdev Kconfig bits
PERS

For instance here I used

@@ -702,6 +703,7 @@ config FB_NVIDIA_DEBUG
 config FB_NVIDIA_BACKLIGHT
        bool "Support for backlight control"
        depends on FB_NVIDIA
+       depends on BACKLIGHT_CLASS_DEVICE=y || BACKLIGHT_CLASS_DEVICE=FB_NVIDIA
        default y
        help
          Say Y here if you want to control the backlight of your display.

while your patch causes a link failure with

CONFIG_FB_NVIDIA=y
CONFIG_FB_NVIDIA_BACKLIGHT=y
CONFIG_BACKLIGHT_CLASS_DEVICE=m

       Arnd