Re: [PATCH v1 2/2] drivers/gpu/drm: don't select DMA_CMA or CMA from aspeed or etnaviv

[David Hildenbrand]

On 08.04.21 12:27, David Hildenbrand wrote:
> On 08.04.21 12:20, Arnd Bergmann wrote:
> > On Thu, Apr 8, 2021 at 11:22 AM David Hildenbrand <david@xxxxxxxxxx> wrote:
> > > Random drivers should not override a user configuration of core knobs
> > > (e.g., CONFIG_DMA_CMA=n). Use "imply" instead, to still respect
> > > dependencies and manual overrides.
> > >
> > > "This is similar to "select" as it enforces a lower limit on another
> > >    symbol except that the "implied" symbol's value may still be set to n
> > >    from a direct dependency or with a visible prompt."
> > >
> > > Implying DRM_CMA should be sufficient, as that depends on CMA.
> > >
> > > Note: If this is a real dependency, we should use "depends on DMA_CMA"
> > > instead -  but I assume the driver can work without CMA just fine --
> > > esp. when we wouldn't have HAVE_DMA_CONTIGUOUS right now.
> >
> > 'imply' is almost never the right solution, and it tends to cause more
> > problems than it solves.
>
> I thought that was the case with "select" :)
>
> > In particular, it does not prevent a configuration with 'DRM_CMA=m'
>
> I assume you meant "DRM_CMA=n" ? DRM_CMA cannot be built as a module.
>
> > and 'DRMA_ASPEED_GFX=y', or any build failures from such
> > a configuration.
>
> I don't follow. "DRM_CMA=n" and 'DRMA_ASPEED_GFX=y' is supposed to work
> just fine (e.g., without HAVE_DMA_CONTIGUOUS) or what am I missing?
>
> > If you want this kind of soft dependency, you need
> > 'depends on DRM_CMA || !DRM_CMA'.
>
> Seriously? I think the point of imply is "please enable if possible and
> not prevented by someone else". Your example looks more like a NOP - no?
> Or will it have the same effect?

I just tried (remove CONFIG_DMA_CMA from .config followed by make) and 
the default will be set to "N" (when querying the user). So it indeed 
looks like a NOP - unless I am missing something.

--
Thanks,

David / dhildenb