From: Arnd Bergmann <arnd@arndb.de>
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>
Subject: Re: [PATCH v1 2/2] drivers/gpu/drm: don't select DMA_CMA or CMA from aspeed or etnaviv
Date: Thu, 8 Apr 2021 12:44:46 +0200 [thread overview]
Message-ID: <CAK8P3a0Wg1mGZoBkD_RwMx-jzQNK2krrDxDQV5uhCHoyz-e=dw@mail.gmail.com> (raw)
In-Reply-To: <cd14d4b4-da82-b21c-2cd6-8e474d97b955@redhat.com>
On Thu, Apr 8, 2021 at 12:29 PM David Hildenbrand <david@redhat.com> wrote:
> On 08.04.21 12:20, Arnd Bergmann wrote:
> > On Thu, Apr 8, 2021 at 11:22 AM David Hildenbrand <david@redhat.com> wrote:
> >>
> >> Random drivers should not override a user configuration of core knobs
> >> (e.g., CONFIG_DMA_CMA=n). Use "imply" instead, to still respect
> >> dependencies and manual overrides.
> >>
> >> "This is similar to "select" as it enforces a lower limit on another
> >> symbol except that the "implied" symbol's value may still be set to n
> >> from a direct dependency or with a visible prompt."
> >>
> >> Implying DRM_CMA should be sufficient, as that depends on CMA.
> >>
> >> Note: If this is a real dependency, we should use "depends on DMA_CMA"
> >> instead - but I assume the driver can work without CMA just fine --
> >> esp. when we wouldn't have HAVE_DMA_CONTIGUOUS right now.
> >
> > 'imply' is almost never the right solution, and it tends to cause more
> > problems than it solves.
>
> I thought that was the case with "select" :)
Yes, but that's a different set of problems
> >
> > 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.
If the problem you are trying to solve is a different one, you need a different
solution, not what I posted above.
> > If you want this kind of soft dependency, you need
> > 'depends on DRM_CMA || !DRM_CMA'.
>
> Seriously? I think the point of imply is "please enable if possible and
> not prevented by someone else".
That used to be the meaning, but it changed a few years ago. Now
it means "when a used manually turns on this symbol, turn on the
implied one as well, but let them turn it off again if they choose".
This is pretty much a NOP.
> 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.
It is a somewhat awkward way to say "prevent this symbol from
being =y if the dependency is =m".
Arnd
next prev parent reply other threads:[~2021-04-08 10:45 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-08 9:20 [PATCH v1 0/2] drivers: don't select DMA_CMA or CMA David Hildenbrand
2021-04-08 9:20 ` [PATCH v1 1/2] drivers/video/fbdev: don't select DMA_CMA David Hildenbrand
2021-04-08 9:56 ` Mike Rapoport
2021-04-08 9:20 ` [PATCH v1 2/2] drivers/gpu/drm: don't select DMA_CMA or CMA from aspeed or etnaviv David Hildenbrand
2021-04-08 9:56 ` Mike Rapoport
2021-04-08 9:57 ` David Hildenbrand
2021-04-08 10:20 ` Arnd Bergmann
2021-04-08 10:27 ` David Hildenbrand
2021-04-08 10:36 ` David Hildenbrand
2021-04-08 10:44 ` Arnd Bergmann [this message]
2021-04-08 11:00 ` David Hildenbrand
2021-04-08 11:44 ` Arnd Bergmann
2021-04-08 12:00 ` David Hildenbrand
2021-04-08 12:12 ` Arnd Bergmann
2021-04-08 12:49 ` Linus Walleij
2021-04-08 13:19 ` Arnd Bergmann
2021-04-09 8:07 ` David Hildenbrand
2021-04-08 16:44 ` David Hildenbrand
2021-04-08 20:29 ` Arnd Bergmann
2021-04-09 8:09 ` David Hildenbrand
2021-04-08 21:45 ` Linus Walleij
2021-04-08 11:38 ` Daniel Vetter
2021-04-08 16:46 ` Jason Gunthorpe
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