netdev - Re: [Freedreno] [PATCH 16/17] iommu: remove DOMAIN_ATTR_IO_PGTABLE

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Message-ID: <20210305100012.GB22536@willie-the-truck>
Date:   Fri, 5 Mar 2021 10:00:12 +0000
From:   Will Deacon <will@...nel.org>
To:     Rob Clark <robdclark@...il.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>, Joerg Roedel <joro@...tes.org>,
        Li Yang <leoyang.li@....com>, kvm@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        virtualization@...ts.linux-foundation.org,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        netdev@...r.kernel.org,
        freedreno <freedreno@...ts.freedesktop.org>,
        David Woodhouse <dwmw2@...radead.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Subject: Re: [Freedreno] [PATCH 16/17] iommu: remove
 DOMAIN_ATTR_IO_PGTABLE_CFG

On Thu, Mar 04, 2021 at 03:11:08PM -0800, Rob Clark wrote:
> On Thu, Mar 4, 2021 at 7:48 AM Robin Murphy <robin.murphy@....com> wrote:
> >
> > On 2021-03-01 08:42, Christoph Hellwig wrote:
> > > Signed-off-by: Christoph Hellwig <hch@....de>
> >
> > Moreso than the previous patch, where the feature is at least relatively
> > generic (note that there's a bunch of in-flight development around
> > DOMAIN_ATTR_NESTING), I'm really not convinced that it's beneficial to
> > bloat the generic iommu_ops structure with private driver-specific
> > interfaces. The attribute interface is a great compromise for these
> > kinds of things, and you can easily add type-checked wrappers around it
> > for external callers (maybe even make the actual attributes internal
> > between the IOMMU core and drivers) if that's your concern.
> 
> I suppose if this is *just* for the GPU we could move it into adreno_smmu_priv..
> 
> But one thing I'm not sure about is whether
> IO_PGTABLE_QUIRK_ARM_OUTER_WBWA is something that other devices
> *should* be using as well, but just haven't gotten around to yet.

The intention is certainly that this would be a place to collate per-domain
pgtable quirks, so I'd prefer not to tie that to the GPU.

Will