Re: [PATCH v2 1/3] fbdev: Fix recursive dependencies wrt BACKLIGHT_CLASS_DEVICE

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi


Am 12.12.24 um 22:04 schrieb Arnd Bergmann:
> On Thu, Dec 12, 2024, at 19:44, Helge Deller wrote:
>> On 12/12/24 11:04, 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 [...]
>> 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'.
>
> I actually have a few more patches like this that I've
> been carrying for years now, e.g. one that changes all the
> 'select I2C' into appropriate dependencies.

Thanks! If you have something for DRM, please submit. In the case of 
i2c, it might happen that the driver is useful without i2c support. But 
that's a discussion for the individual reviews.

Best regards
Thomas

>
>         Arnd

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
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