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SubjectRe: [PATCH v2] fbdev: Prevent probing generic drivers if a FB is already registered
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Hello Geert,

On 11/16/21 10:43, Geert Uytterhoeven wrote:

[snip]

>>
>> So this is already a fragile solution and $SUBJECT doesn't make things worse
>> IMO. Since not having something like this can lead to issues as reported by:
>>
>> https://lore.kernel.org/all/20211110200253.rfudkt3edbd3nsyj@lahvuun/
>>
>> We could probably do some smarter here by providing a function that checks
>> if the registered fbdev drivers matches the aperture base. But I'm unsure
>> if that's worth it. After all, fbdev drivers are likely to be disabled by
>> most distros soon now that we have the simpledrm driver.
>
> Checking the aperture base is what was done in all other cases of
> preventing generic (fbdev) drivers from stepping on specific drivers'
> toes...
>

Ok, I can re-spin the patch checking if the aperture ranges overlap. There's
an apertures_overlap() function in drivers/video/fbdev/core/fbmem.c that can
be exported for fbdev drivers to use.

Another option is to just say that DRM drivers should be built as a module if
the {efi,simple}fb driver are built-in.

Best regards,
--
Javier Martinez Canillas
Linux Engineering
Red Hat

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