clearly mark DMA_OPS support as an architecture feasture

[Jason Wang]

On Sat, Aug 24, 2024 at 11:58 AM Christoph Hellwig <hch at lst.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.

Thanks