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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 8 Apr 2021 13:44:22 +0200
Message-ID: <CAK8P3a1tVwkDbtvKi8atkrg1-CfoQHGrXLCzn_uo+=dfZJfdQA@mail.gmail.com>
Subject: Re: [PATCH v1 2/2] drivers/gpu/drm: don't select DMA_CMA or CMA from
 aspeed or etnaviv
To:     David Hildenbrand <david@redhat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>, Joel Stanley <joel@jms.id.au>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andrew Jeffery <andrew@aj.id.au>,
        Lucas Stach <l.stach@pengutronix.de>,
        Russell King <linux+etnaviv@armlinux.org.uk>,
        Christian Gmeiner <christian.gmeiner@gmail.com>,
        Mike Rapoport <rppt@kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Michal Simek <michal.simek@xilinx.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Peter Collingbourne <pcc@google.com>,
        linux-aspeed <linux-aspeed@lists.ozlabs.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        The etnaviv authors <etnaviv@lists.freedesktop.org>,
        Linux Fbdev development list <linux-fbdev@vger.kernel.org>
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On Thu, Apr 8, 2021 at 1:00 PM David Hildenbrand <david@redhat.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