linux-kernel - Re: [PATCH v1 2/2] drivers/gpu/drm: don't select DMA

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Date:   Thu, 8 Apr 2021 18:44:23 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        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>,
        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

On 08.04.21 14:49, Linus Walleij wrote:
> On Thu, Apr 8, 2021 at 2:01 PM David Hildenbrand <david@...hat.com> wrote:
> 
>>> 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 !)
> 
> If you do this it probably makes sense to fix a few other drivers
> Kconfig in the process. It's not just a problem with your driver.
> "my" drivers:
> 

:) I actually wanted to convert them to "depends on DMA_CMA" but ran 
into recursive dependencies ...

> drivers/gpu/drm/mcde/Kconfig
> drivers/gpu/drm/pl111/Kconfig
> drivers/gpu/drm/tve200/Kconfig

I was assuming these are "real" dependencies. Will it also work without 
DMA_CMA?

> 
> certainly needs this as well, and pretty much anything that is
> selecting DRM_KMS_CMA_HELPER or
> DRM_GEM_CMA_HELPER "wants" DMA_CMA.

"wants" as in "desires to use but can life without" or "wants" as in 
"really needs it". ?

-- 
Thanks,

David / dhildenb