On 12/13/24 00:24, Jani Nikula wrote:

On Thu, 12 Dec 2024, "Arnd Bergmann" [off-list ref] wrote:

quoted

On Thu, Dec 12, 2024, at 19:44, Helge Deller wrote:

quoted

On 12/12/24 11:04, Thomas Zimmermann wrote:

quoted

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 [...]

I think in the fbdev drivers themselves you should do:
	select BACKLIGHT_CLASS_DEVICE
instead of "depending" on it.
This is the way as it's done in the DRM tiny and the i915/gma500 DRM drivers.

So, something like:

--- a/drivers/staging/fbtft/Kconfig
         tristate "Support for small TFT LCD display modules"
         depends on FB && SPI
         depends on FB_DEVICE
    +    select BACKLIGHT_DEVICE_CLASS
         depends on GPIOLIB || COMPILE_TEST
         select FB_BACKLIGHT

config FB_BACKLIGHT
            tristate
            depends on FB
    -	  select BACKLIGHT_CLASS_DEVICE
    +       depends on BACKLIGHT_CLASS_DEVICE


Would that fix the dependency warning?

The above is generally a mistake and the root cause of the
dependency loops. With very few exceptions, the solution in
these cases is to find the inconsistent 'select' and change
it into 'depends on'.

Agreed.

That's fine, but my point is that it should be consistent.
For example:

~:/git-kernel/linux$ grep -r "select.*BACKLIGHT_CLASS_DEVICE" drivers/gpu/
drivers/gpu/drm/tilcdc/Kconfig: select BACKLIGHT_CLASS_DEVICE
drivers/gpu/drm/nouveau/Kconfig:        select BACKLIGHT_CLASS_DEVICE if DRM_NOUVEAU_BACKLIGHT
drivers/gpu/drm/nouveau/Kconfig:        select BACKLIGHT_CLASS_DEVICE if ACPI && X86
drivers/gpu/drm/tiny/Kconfig:   select BACKLIGHT_CLASS_DEVICE
drivers/gpu/drm/tiny/Kconfig:   select BACKLIGHT_CLASS_DEVICE
drivers/gpu/drm/tiny/Kconfig:   select BACKLIGHT_CLASS_DEVICE
drivers/gpu/drm/tiny/Kconfig:   select BACKLIGHT_CLASS_DEVICE
drivers/gpu/drm/tiny/Kconfig:   select BACKLIGHT_CLASS_DEVICE
drivers/gpu/drm/tiny/Kconfig:   select BACKLIGHT_CLASS_DEVICE
drivers/gpu/drm/tiny/Kconfig:   select BACKLIGHT_CLASS_DEVICE
drivers/gpu/drm/fsl-dcu/Kconfig:        select BACKLIGHT_CLASS_DEVICE
drivers/gpu/drm/i915/Kconfig:   select BACKLIGHT_CLASS_DEVICE if ACPI
drivers/gpu/drm/gma500/Kconfig: select BACKLIGHT_CLASS_DEVICE if ACPI
drivers/gpu/drm/amd/amdgpu/Kconfig:     select BACKLIGHT_CLASS_DEVICE
drivers/gpu/drm/xe/Kconfig:     select BACKLIGHT_CLASS_DEVICE if ACPI
drivers/gpu/drm/solomon/Kconfig:        select BACKLIGHT_CLASS_DEVICE
drivers/gpu/drm/radeon/Kconfig: select BACKLIGHT_CLASS_DEVICE
drivers/gpu/drm/renesas/shmobile/Kconfig:       select BACKLIGHT_CLASS_DEVICE
drivers/gpu/drm/gud/Kconfig:    select BACKLIGHT_CLASS_DEVICE
drivers/gpu/drm/bridge/Kconfig: select BACKLIGHT_CLASS_DEVICE

All major drm graphics drivers *select* BACKLIGHT_CLASS_DEVICE.
Are you changing them to "depend on" as well?

Helge