linux-kernel - Re: [PATCH v1 05/14] iommu/arm-smmu-v3: Remove ARM_SMMU_DOMAIN

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Date:   Fri, 10 Mar 2023 16:23:25 -0800
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Eric Auger <eric.auger@...hat.com>
CC:     <jgg@...dia.com>, <robin.murphy@....com>, <will@...nel.org>,
        <kevin.tian@...el.com>, <baolu.lu@...ux.intel.com>,
        <joro@...tes.org>, <shameerali.kolothum.thodi@...wei.com>,
        <jean-philippe@...aro.org>, <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 05/14] iommu/arm-smmu-v3: Remove ARM_SMMU_DOMAIN_NESTED

On Fri, Mar 10, 2023 at 05:39:22PM +0100, Eric Auger wrote:
> External email: Use caution opening links or attachments
> 
> 
> Hi Nicolin,
> 
> On 3/9/23 11:53, Nicolin Chen wrote:
> > IOMMUFD designs two iommu_domain pointers to represent two stages. The S1
> s/designs/uses?
> > iommu_domain (IOMMU_DOMAIN_NESTED type) represents the Context Descriptor
> > table in the user space. The S2 iommu_domain (IOMMU_DOMAIN_UNMANAGED type)
> > represents the translation table in the kernel, owned by a hypervisor.
> >
> > So there comes to no use case of the ARM_SMMU_DOMAIN_NESTED. Drop it, and
> > use the type IOMMU_DOMAIN_NESTED instead.
> last sentence may be rephrased as this patch does not use
> IOMMU_DOMAIN_NESTED anywhere:
> Generic IOMMU_DOMAIN_NESTED type will be used in nested SMMU
> implementation instead.
> >
> > Also drop the unused arm_smmu_enable_nesting(). One following patche will
> > configure the correct smmu_domain->stage.
> >
> > Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> > ---
> >  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 18 ------------------
> >  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h |  1 -
> If you go this way you may also remove it from arm/arm-smmu/arm-smmu.c.
> Then if I am not wrong no other driver does implement enable_nesting cb.
> Shouldn't we also remove it and fellow iommu_enable_nesting()?

We had a small discussion before this community version, where
Robin mentioned that we can remove that too after the nesting
series gets merged. Yet, I didn't want to touch the v2 driver
with this series since there's no nesting change adding to it.

And a few month ago, Jason had a patch removing everything of
that API from the top. Perhaps that one can be resent after
all?

Thanks
Nic