linux-kernel - Re: [PATCH v3 1/4] iommu: Introduce device_iommu

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Date:   Wed, 6 Apr 2022 07:28:12 +0200
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     joro@...tes.org, baolu.lu@...ux.intel.com,
        andreas.noever@...il.com, michael.jamet@...el.com,
        mika.westerberg@...ux.intel.com, YehezkelShB@...il.com,
        iommu@...ts.linux-foundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, mario.limonciello@....com, hch@....de
Subject: Re: [PATCH v3 1/4] iommu: Introduce device_iommu_capable()

On Tue, Apr 05, 2022 at 11:41:01AM +0100, Robin Murphy wrote:
> iommu_capable() only really works for systems where all IOMMU instances
> are completely homogeneous, and all devices are IOMMU-mapped. Implement
> the new variant which can give an accurate answer for whichever device
> the caller is actually interested in.
> 
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
> 
> v3: New patch; now that the dev_iommu_ops() work has landed we can go
>     straight to a proper implementation. Also s/dev/device/ to match
>     the precedent of device_iommu_mapped() for the public API.

I'm a little worrited about a method with a parameter than can be
NULL.

Also usnic, vmd, and vdpa really want to use your new
device_iommu_capable as they check based on a device.  Just VFIO
is special as usual..