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

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Date:   Thu, 8 Apr 2021 14:49:51 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     David Hildenbrand <david@...hat.com>
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 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:

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

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

Yours,
Linus Walleij