Re: [PATCH] iommu/vt-d: Remove an unnecessary call set_dma_ops()

[Robin Murphy <robin.murphy@arm.com>]

On 10/04/2025 3:59 am, Baolu Lu wrote:
> On 4/9/25 23:44, Petr Tesařík wrote:
>> On Thu,  3 Apr 2025 18:56:05 +0200
>> Petr Tesarik<ptesarik@suse.com> wrote:
>>
>>> Do not touch per-device DMA ops when the driver has been converted to 
>>> use
>>> the dma-iommu API.
>>>
>>> Fixes: c588072bba6b ("iommu/vt-d: Convert intel iommu driver to the 
>>> iommu ops")
>>> Signed-off-by: Petr Tesarik<ptesarik@suse.com>
>> Does anyone agree? Or see any issues?

At least it definitely serves no purpose since b5c58b2fdc42 
("dma-mapping: direct calls for dma-iommu"). FWIW,

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> This change looks good to me. The iommu driver should not call
> set_dma_ops() anyway. I will queue this for v6.15-rc.
> 
> I ever wondered whether we could clean up dev->dma_iommu when the device
> is released by the iommu core. But, iommu_release_device() is only
> called in the device removal path, so keeping dev->dma_iommu set doesn't
> impose any functional impact AFAICS.

Funnily enough I've just been looking at that - I'd long held the same 
assumption, but I'd been forgetting the edge case that's always been 
there if bus_set_iommu(), and now iommu_device_register(), failed and 
groups and default domains were torn down for existing devices. So in 
fact it seems Intel was one of the few drivers/architectures managing to 
do the right thing before :)

Cheers,
Robin.