[PATCH v3 1/3] fbdev: Fix recursive dependencies wrt BACKLIGHT_CLASS_DEVICE

[Arnd Bergmann]

On Sun, Dec 22, 2024, at 21:15, Helge Deller wrote:
> On 12/22/24 17:09, Thomas Zimmermann wrote:

>>>> +    depends on BACKLIGHT_CLASS_DEVICE=y || BACKLIGHT_CLASS_DEVICE=FB_NVIDIA
>>>
>>> Seems wrong. BACKLIGHT_CLASS_DEVICE is of type tristate.
>>> There are more of those, please check.
>>
>> It's exactly correct. Linking would fail with FB_NVIDIA=y and BACKLIGHT=m. The above construct avoids this case. Please see Arnd's review comment at [1].
>
> I'm not arguing against "depends on BACKLIGHT_CLASS_DEVICE=y".
> It's the "BACKLIGHT_CLASS_DEVICE=FB_NVIDIA" which is wrong.
> BACKLIGHT_CLASS_DEVICE is tristate, so either "y", "n" or "m", but 
> never "FB_NVIDIA".

There are multiple ways to express this, but that line is a correct
way to allow all of

  BACKLIGHT_CLASS_DEVICE=y, FB_NVIDIA=m, FB_NVIDIA_BACKLIGHT=y
  BACKLIGHT_CLASS_DEVICE=y, FB_NVIDIA=y, FB_NVIDIA_BACKLIGHT=y
  BACKLIGHT_CLASS_DEVICE=m, FB_NVIDIA=m, FB_NVIDIA_BACKLIGHT=y

but disallow the broken

  BACKLIGHT_CLASS_DEVICE=m, FB_NVIDIA=y, FB_NVIDIA_BACKLIGHT=y

If you find this line too confusing, can you suggest a different
expression that has the same behavior?

       Arnd