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Date:   Thu, 8 Apr 2021 13:00:47 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, Joel Stanley <joel@....id.au>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Andrew Jeffery <andrew@...id.au>,
        Lucas Stach <l.stach@...gutronix.de>,
        Russell King <linux+etnaviv@...linux.org.uk>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        Mike Rapoport <rppt@...nel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Michal Simek <michal.simek@...inx.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Peter Collingbourne <pcc@...gle.com>,
        linux-aspeed <linux-aspeed@...ts.ozlabs.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        The etnaviv authors <etnaviv@...ts.freedesktop.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>
Subject: Re: [PATCH v1 2/2] drivers/gpu/drm: don't select DMA_CMA or CMA from
 aspeed or etnaviv

>>> 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.
> 
> Ok, at least that makes it easier.
> 
>>> 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?
> 
> I thought you were trying to solve the problem where DRMA_ASPEED_GFX
> can optionally link against CMA but would fail to build when the CMA code
> is in a loadable module.

Yes. I was trying to say: it works with this patch just fine. The issue 
you described does not seem to apply (DRM_CMA=m).

> 
>> Your example looks more like a NOP - no?
>> Or will it have the same effect?
> 
> The example I gave is only meaningful if both are tristate, which is
> not the case here as you explain.

Okay, thanks.

> 
> 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.

Thanks!

-- 
Thanks,

David / dhildenb

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