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

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Message-ID: <4b33b50f-f0c3-4db8-b394-dd2d4d6e3a55@collabora.com>
Date: Wed, 21 Jan 2026 14:50:18 +0100
From: Benjamin Gaignard <benjamin.gaignard@...labora.com>
To: Will Deacon <will@...nel.org>
Cc: joro@...tes.org, robin.murphy@....com, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, heiko@...ech.de,
 nicolas.dufresne@...labora.com, p.zabel@...gutronix.de, mchehab@...nel.org,
 iommu@...ts.linux.dev, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-rockchip@...ts.infradead.org, linux-media@...r.kernel.org,
 kernel@...labora.com
Subject: Re: [PATCH v11 3/7] iommu: Add verisilicon IOMMU driver


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
>