linux-kernel - Re: [Freedreno] [PATCH v12 04/13] iommu: Add a domain attribute to get/set a pagetable configuration

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Date:   Thu, 13 Aug 2020 08:11:02 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Will Deacon <will@...nel.org>
Cc:     Jordan Crouse <jcrouse@...eaurora.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Freedreno] [PATCH v12 04/13] iommu: Add a domain attribute to
 get/set a pagetable configuration

On Thu, Aug 13, 2020 at 6:14 AM Will Deacon <will@...nel.org> wrote:
>
> On Mon, Aug 10, 2020 at 04:26:48PM -0600, Jordan Crouse wrote:
> > Add domain attribute DOMAIN_ATTR_PGTABLE_CFG. This will be used by
> > arm-smmu to share the current pagetable configuration with the
> > leaf driver and to allow the leaf driver to set up a new pagetable
> > configuration under certain circumstances.
> >
> > Signed-off-by: Jordan Crouse <jcrouse@...eaurora.org>
> > ---
> >
> >  include/linux/iommu.h | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index fee209efb756..995ab8c47ef2 100644
> > --- a/include/linux/iommu.h
> > +++ b/include/linux/iommu.h
> > @@ -118,6 +118,7 @@ enum iommu_attr {
> >       DOMAIN_ATTR_FSL_PAMUV1,
> >       DOMAIN_ATTR_NESTING,    /* two stages of translation */
> >       DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
> > +     DOMAIN_ATTR_PGTABLE_CFG,
> >       DOMAIN_ATTR_MAX,
> >  };
>
> Nobody other than the adreno gpu uses this, so can we avoid exposing it
> in the IOMMU API, please? Given that you have a reference to the adreno
> GPU device in the SMMU implementation code thanks to .alloc_context_bank(),
> can you squirrel some function pointers away in the driver data (i.e. with
> dev_set_drvdata()) instead?
>

Hmm, we are already using drvdata on the gpu side, and it looks like
arm-smmu is also using it.  Could we get away with stashing an extra
'void *' in iommu_domain itself?

Or alternatively, if we had a is_arm_smmu_domain(domain), then we
could just directly call some exported private fxns with the domain
ptr (which could then verify that the domain is actually an
arm_smmu_domain, and then from there that the smmu is indeed
qcom,adreno-smmu, to keep things sane)

BR,
-R