Re: [RFC 1/1] xen/arm: set iommu property for IOMMU-protected devices

[Julien Grall <julien@xxxxxxx>]

Hi Roman,

On 04/10/2021 10:54, Roman Skakun wrote:
> From: Roman Skakun <roman_skakun@xxxxxxxx>
>
> Xen is not exposing any IOMMU properties to Dom0.
> So Dom0 assumes that all it's devices are not protected by IOMMU.
>
> To make Dom0 aware of IOMMU-protected devices, we need to mark
> them somehow. With this approach Dom0 Linux kernel will be able
> to selectively disable swiotlb-xen fops for them which will remove
> unnecessary buffer bounces.
>
> This patch adds mechanism to describe IOMMU-protected devices by
> adding `xen,behind-iommu` property to relevant device nodes in
> Dom0 device tree.
A few years ago, I attempted to disable the swiotlb when Xen configured 
the IOMMU for the device (see [1]). Did you have a chance to go through 
the thread? In particular, I think Ian Campbell suggestion about 
creating an IOMMU binding is quite interesting.
Stefano, what do you think?

Cheers,

[1] 
https://patchwork.ozlabs.org/project/devicetree-bindings/patch/1392913301-25524-1-git-send-email-julien.grall@xxxxxxxxxx/
--
Julien Grall