linux-kernel - Re: [PATCH] dma-mapping: Stub out dma_{alloc,free,map}

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Message-ID: <5f1ca0ac-b66c-4b92-8f69-027c2468b117@sirena.org.uk>
Date: Mon, 16 Jun 2025 13:06:00 +0100
From: Mark Brown <broonie@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: James Clark <james.clark@...aro.org>, olteanv@...il.com,
	oe-kbuild-all@...ts.linux.dev, arnd@...db.de,
	larisa.grigore@....com, Frank.li@....com, linux-spi@...r.kernel.org,
	imx@...ts.linux.dev, linux-kernel@...r.kernel.org,
	kernel test robot <lkp@...el.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>, iommu@...ts.linux.dev
Subject: Re: [PATCH] dma-mapping: Stub out dma_{alloc,free,map}_pages() API

On Mon, Jun 16, 2025 at 01:29:27PM +0200, Christoph Hellwig wrote:
> On Mon, Jun 16, 2025 at 12:17:49PM +0100, James Clark wrote:

> > The implementations are in mapping.c which requires HAS_DMA so stub them
> > out if not present. This is required for some drivers to pass randconfig
> > builds.

> No.  Just add the proper IS_ENABLED checks in the callers.  While these
> kinds of stubs used to be popular they are really nasty in that the
> calls unexpectedly just fail without the right depends.

The issue with HAS_DMA is that essentially all platforms have and rely
on DMA.  This ends up just being painful noise from the buildbots when
they do randconfigs rather than something useful.

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