linux-kernel - Re: [PATCH 1/2] iommu/arm-smmu-qcom: Skip the TTBR1 quirk for db820c.

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Message-ID: <CAF6AEGs+gUZ+5kmyA0Xz4jz8QJRgLVfaWmvQzuwXZBBG4xAr5w@mail.gmail.com>
Date:   Tue, 30 Mar 2021 09:07:18 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Will Deacon <will@...nel.org>
Cc:     Eric Anholt <eric@...olt.net>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Sean Paul <sean@...rly.run>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Robin Murphy <robin.murphy@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Joerg Roedel <joro@...tes.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] iommu/arm-smmu-qcom: Skip the TTBR1 quirk for db820c.

On Tue, Mar 30, 2021 at 8:31 AM Will Deacon <will@...nel.org> wrote:
>
> On Tue, Mar 30, 2021 at 08:03:36AM -0700, Rob Clark wrote:
> > On Tue, Mar 30, 2021 at 2:34 AM Will Deacon <will@...nel.org> wrote:
> > >
> > > On Mon, Mar 29, 2021 at 09:02:50PM -0700, Rob Clark wrote:
> > > > On Mon, Mar 29, 2021 at 7:47 AM Will Deacon <will@...nel.org> wrote:
> > > > >
> > > > > On Fri, Mar 26, 2021 at 04:13:02PM -0700, Eric Anholt wrote:
> > > > > > db820c wants to use the qcom smmu path to get HUPCF set (which keeps
> > > > > > the GPU from wedging and then sometimes wedging the kernel after a
> > > > > > page fault), but it doesn't have separate pagetables support yet in
> > > > > > drm/msm so we can't go all the way to the TTBR1 path.
> > > > >
> > > > > What do you mean by "doesn't have separate pagetables support yet"? The
> > > > > compatible string doesn't feel like the right way to determine this.
> > > >
> > > > the compatible string identifies what it is, not what the sw
> > > > limitations are, so in that regard it seems right to me..
> > >
> > > Well it depends on what "doesn't have separate pagetables support yet"
> > > means. I can't tell if it's a hardware issue, a firmware issue or a driver
> > > issue.
> >
> > Just a driver issue (and the fact that currently we don't have
> > physical access to a device... debugging a5xx per-process-pgtables by
> > pushing untested things to the CI farm is kind of a difficult way to
> > work)
>
> But then in that case, this is using the compatible string to identify a
> driver issue, no?
>

Well, I suppose yes.. but OTOH it is keeping the problem out of the
dtb.  Once per-process pgtables works for a5xx, there would be no dtb
change, just a change to the quirk behavior in arm-smmu-qcom.

BR,
-R