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

On 08.04.21 13:44, Arnd Bergmann wrote:

On Thu, Apr 8, 2021 at 1:00 PM David Hildenbrand [off-list ref] wrote:

quoted

quoted

It is a somewhat awkward way to say "prevent this symbol from
being =y if the dependency is =m".

What would be the right thing to do in the case here then to achieve the
"if DRMA_ASPEED_GFX is enabled, also enable DMA_CMA id possible"?

One approach could be to have for DMA_CMA

default y if DRMA_ASPEED_GFX

but it feels like the wrong way to tackle this.

I'm still not sure what you are trying to achieve. Is the idea only to provide
a useful default for DMA_CMA depending on which drivers are enabled?

"Random drivers should not override a user configuration of core knobs
(e.g., CONFIG_DMA_CMA=n)."

Let's assume I'm a distribution and want to set CONFIG_CMA=n or want to 
set CONFIG_DMA_CMA=n with CONFIG_CMA=y; there is no way to do that with 
e.g., DRMA_ASPEED_GFX=y because it will always override my (user!) 
setting -- even though it doesn't really always need it. Using "select" 
is the problem here.

This is something you could do using a hidden helper symbol like

config DRMA_ASPEED_GFX
        bool "Aspeed display driver"
        select DRM_WANT_CMA

config DRM_WANT_CMA
        bool
        help
           Select this from any driver that benefits from CMA being enabled

config DMA_CMA
        bool "Use CMA helpers for DRM"
        default DRM_WANT_CMA

          Arnd

That's precisely what I had first, with an additional "WANT_CMA" --  but 
looking at the number of such existing options (I was able to spot 1 !) 
I wondered if there is a better approach to achieve the same; "imply" 
sounded like a good candidate.

-- 
Thanks,

David / dhildenb


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