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Thu, 8 Apr 2021 12:00:49 +0000 (UTC) Subject: Re: [PATCH v1 2/2] drivers/gpu/drm: don't select DMA_CMA or CMA from aspeed or etnaviv To: Arnd Bergmann Cc: Linux Kernel Mailing List , Linux-MM , Joel Stanley , David Airlie , Daniel Vetter , Andrew Jeffery , Lucas Stach , Russell King , Christian Gmeiner , Mike Rapoport , Bartlomiej Zolnierkiewicz , Linus Walleij , Michal Simek , Masahiro Yamada , Randy Dunlap , Peter Collingbourne , linux-aspeed , dri-devel , Linux ARM , The etnaviv authors , Linux Fbdev development list References: <20210408092011.52763-1-david@redhat.com> <20210408092011.52763-3-david@redhat.com> <7496ac87-9676-1b4e-3444-c2a662ec376b@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <3a2d64a7-8425-8daf-17ee-95b9f0c635f9@redhat.com> Date: Thu, 8 Apr 2021 14:00:48 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Stat-Signature: ggju38ou96qeyapju8fu3jtdhhpx38uu X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: DAEC7A0049D9 Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf24; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=216.205.24.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617883281-762825 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 08.04.21 13:44, Arnd Bergmann wrote: > On Thu, Apr 8, 2021 at 1:00 PM David Hildenbrand 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? "Random drivers should not override a user configuration of core knobs (e.g., CONFIG_DMA_CMA=n)." Let's assume I'm a distribution and want to set CONFIG_CMA=n or want to set CONFIG_DMA_CMA=n with CONFIG_CMA=y; there is no way to do that with e.g., DRMA_ASPEED_GFX=y because it will always override my (user!) setting -- even though it doesn't really always need it. Using "select" is the problem here. > > 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 !) I wondered if there is a better approach to achieve the same; "imply" sounded like a good candidate. -- Thanks, David / dhildenb