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

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Message-ID: <CAK8P3a1tVwkDbtvKi8atkrg1-CfoQHGrXLCzn_uo+=dfZJfdQA@mail.gmail.com>
Date:   Thu, 8 Apr 2021 13:44:22 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     David Hildenbrand <david@...hat.com>
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

On Thu, Apr 8, 2021 at 1:00 PM David Hildenbrand <david@...hat.com> wrote:
> >
> > 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?

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