linux-kernel - Re: clearly mark DMA_OPS support as an architecture feasture

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Message-ID: <CACGkMEu83MjTpkSS1mX02ar8RNDc5T4bsd4kkGHYhkH7LZY-wA@mail.gmail.com>
Date: Mon, 26 Aug 2024 14:27:27 +0800
From: Jason Wang <jasowang@...hat.com>
To: Christoph Hellwig <hch@....de>, "Michael S . Tsirkin" <mst@...hat.com>
Cc: iommu@...ts.linux.dev, Marek Szyprowski <m.szyprowski@...sung.com>, 
	Robin Murphy <robin.murphy@....com>, Sakari Ailus <sakari.ailus@...ux.intel.com>, 
	Bingbu Cao <bingbu.cao@...el.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: Re: clearly mark DMA_OPS support as an architecture feasture

On Mon, Aug 26, 2024 at 2:16 PM Jason Wang <jasowang@...hat.com> wrote:
>
> On Sat, Aug 24, 2024 at 11:58 AM Christoph Hellwig <hch@....de> wrote:
> >
> > 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_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).
> >
>
> I will try to fix the simulator considering virtio has already had
> mapping ops now.

Actually I meant, we can extend the virtio_config_ops to allow mapping
ops there, then simulator and VDUSE can hook the map ops there.

Not sure if Michael is fine with this.

Thanks

>
> Thanks