linux-kernel - clearly mark DMA_OPS support as an architecture feature v2

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Message-ID: <20240828061104.1925127-1-hch@lst.de>
Date: Wed, 28 Aug 2024 09:10:27 +0300
From: Christoph Hellwig <hch@....de>
To: iommu@...ts.linux.dev
Cc: Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Bingbu Cao <bingbu.cao@...el.com>,
	"Michael S . Tsirkin " <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	linux-kernel@...r.kernel.org,
	linux-alpha@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mips@...r.kernel.org,
	linux-parisc@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org,
	linux-s390@...r.kernel.org,
	sparclinux@...r.kernel.org,
	linux-media@...r.kernel.org,
	virtualization@...ts.linux.dev,
	xen-devel@...ts.xenproject.org
Subject: clearly mark DMA_OPS support as an architecture feature v2

Hi all,

we've had a long standing problems where drivers try to hook into the
DMA_OPS mechanisms to override them for something that is not DMA, or
to introduce additional dispatching.

Now that we are not using DMA_OPS support for dma-iommu and can build
kernels without DMA_OPS support on many common setups this becomes even
more problematic.

This series renames the option to ARCH_HAS_DMA_OPS and adds very explicit
comment to not use it in drivers.  The ipu6 and vdpa_sim/user drivers
that abuse the mechanism are made to depend on the option instead of
selecting it with a big comment, but I expect this to be fixed rather
sooner than later (I know the ipu6 maintainers are on it based on a
previous discussion).

Changes since v1:
 - s/ARCH_DMA_OPS/ARCH_HAS_DMA_OPS/g
 - spelling fixes
 - vdpa_sim actually doesn't need dma ops these days, add a prep patch
   to remove the dependency