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From: David Hildenbrand <david@redhat.com>
To: Arnd Bergmann <arnd@arndb.de>
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 12:36:59 +0200	[thread overview]
Message-ID: <0b1928a8-99c3-f1f1-ad66-40145199d9bc@redhat.com> (raw)
In-Reply-To: <cd14d4b4-da82-b21c-2cd6-8e474d97b955@redhat.com>

On 08.04.21 12:27, David Hildenbrand 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" :)
> 
>>
>> 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.
> 
>> 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?
> 
>>
>> 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". Your example looks more like a NOP - no?
> Or will it have the same effect?

I just tried (remove CONFIG_DMA_CMA from .config followed by make) and 
the default will be set to "N" (when querying the user). So it indeed 
looks like a NOP - unless I am missing something.

-- 
Thanks,

David / dhildenb


  reply	other threads:[~2021-04-08 10:37 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 [this message]
2021-04-08 10:44       ` Arnd Bergmann
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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