Re: [PATCH v11 3/7] iommu: Add verisilicon IOMMU driver

[Benjamin Gaignard]

Le 21/01/2026 à 13:51, Will Deacon a écrit :
> On Mon, Jan 19, 2026 at 03:03:44PM +0100, Benjamin Gaignard wrote:
> > > > > > > > +static const struct iommu_ops vsi_iommu_ops = {
> > > > > > > > +	.identity_domain = &vsi_identity_domain,
> > > > > > > > +	.release_domain = &vsi_identity_domain,
> > > > > > > > +	.domain_alloc_paging = vsi_iommu_domain_alloc_paging,
> > > > > > > > +	.of_xlate = vsi_iommu_of_xlate,
> > > > > > > > +	.probe_device = vsi_iommu_probe_device,
> > > > > > > > +	.release_device = vsi_iommu_release_device,
> > > > > > > > +	.device_group = generic_single_device_group,
> > > > > > > > +	.owner = THIS_MODULE,
> > > > > > > > +	.default_domain_ops = &(const struct iommu_domain_ops) {
> > > > > > > > +		.attach_dev		= vsi_iommu_attach_device,
> > > > > > > > +		.map_pages		= vsi_iommu_map,
> > > > > > > > +		.unmap_pages		= vsi_iommu_unmap,
> > > > > > > > +		.flush_iotlb_all	= vsi_iommu_flush_tlb_all,
> > > > > > > This has no callers and so your unmap routine appears to be broken.
> > > > > > It is a leftover of previous attempt to allow video decoder to clean/flush
> > > > > > the iommu by using a function from the API.
> > > > > > Now it is using vsi_iommu_restore_ctx().
> > > > > > I while remove it in version 12.
> > > > > Don't you still need some invalidation on the unmap path?
> > > > In vsi_iommu_unmap_iova() page is invalided by calling vsi_mk_pte_invalid().
> > > But that just writes an invalid descriptor and doesn't appear to invalidate
> > > the TLB at all.
> > >
> > > > That clear BIT(0) so the hardware knows the page is invalid.
> > > > Do I have miss something here ?
> > > Yes, the TLB structure needs to be invalidated so that the page-table
> > > walker sees the new value that you have written in memory.
> > >
> > > The rockchip driver gets this correct...
> > Rockchip hardware have a ZAP_ONE_LINE register which didn't exist on Verisilicon
> > hardware.
> Presumably you have some sort of Verisilicon datasheet or downstream driver
> from which you can infer the TLB invalidation runes?

I have only this downstream driver:
https://github.com/rockchip-linux/kernel/blob/develop-6.1/drivers/iommu/rockchip-iommu-av1d.c
No datasheet...

> > I have tried to use VSI_MMU_BIT_FLUSH on VSI driver after unmapping iova
> > but it doesn't work.
> What do you mean by "doesn't work"? If it works without doing any
> invalidation at all, then it's very peculiar that adding the invalidation
> would introduce issues.

I mean VSI_MMU_BIT_FLUSH register can't be used to invalid the TLB.
I think the hardware iterates over the pages tables in memory and
check the valid/invalid bit.

Benjamin

> > So far calling dma_sync_single_for_device() seems to be enough to make iommu
> > and video decoder work together.
> I don't think we should settle for "seems to enough"! If we can reason
> about the operation of the hardware then the driver will be undebuggable
> when it eventually goes wrong.
>
> Will