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SubjectRe: [RFC PATCH 06/11] iommu: arm-smmu: Remove Calxeda secure mode quirk
On Fri, 28 Feb 2020 10:50:25 +0000
Will Deacon <will@kernel.org> wrote:

> On Fri, Feb 28, 2020 at 10:25:56AM +0000, Andre Przywara wrote:
> > On Fri, 28 Feb 2020 10:04:47 +0000
> > Will Deacon <will@kernel.org> wrote:
> >
> > Hi,
> >
> > > On Tue, Feb 25, 2020 at 04:01:54PM -0600, Rob Herring wrote:
> > > > On Tue, Feb 18, 2020 at 11:20 AM Will Deacon <will@kernel.org> wrote:
> > > > >
> > > > > On Tue, Feb 18, 2020 at 11:13:16AM -0600, Rob Herring wrote:
> > > > > > Cc: Will Deacon <will@kernel.org>
> > > > > > Cc: Robin Murphy <robin.murphy@arm.com>
> > > > > > Cc: Joerg Roedel <joro@8bytes.org>
> > > > > > Cc: iommu@lists.linux-foundation.org
> > > > > > Signed-off-by: Rob Herring <robh@kernel.org>
> > > > > > ---
> > > > > > Do not apply yet.
> > > > >
> > > > > Pleeeeease? ;)
> > > > >
> > > > > > drivers/iommu/arm-smmu-impl.c | 43 -----------------------------------
> > > > > > 1 file changed, 43 deletions(-)
> > > > >
> > > > > Yes, I'm happy to get rid of this. Sadly, I don't think we can remove
> > > > > anything from 'struct arm_smmu_impl' because most implementations fall
> > > > > just short of perfect.
> > > > >
> > > > > Anyway, let me know when I can push the button and I'll queue this in
> > > > > the arm-smmu tree.
> > > >
> > > > Seems we're leaving the platform support for now, but I think we never
> > > > actually enabled SMMU support. It's not in the dts either in mainline
> > > > nor the version I have which should be close to what shipped in
> > > > firmware. So as long as Andre agrees, this one is good to apply.
> > >
> > > Andre? Can I queue this one for 5.7, please?
> >
> > I was wondering how much of a pain it is to keep it in? AFAICS there are
> > other users of the "impl" indirection. If those goes away, I would be
> > happy to let Calxeda go.
>
> The impl stuff is new, so we'll keep it around. The concern is more about
> testing (see below).
>
> > But Eric had the magic DT nodes to get the SMMU working, and I used that
> > before, with updating the DT either on flash or dynamically via U-Boot.
>
> What did you actually use the SMMU for, though? The
> 'arm_iommu_create_mapping()' interface isn't widely used and, given that
> highbank doesn't support KVM, the use-cases for VFIO are pretty limited
> too.

AFAIK Highbank doesn't have the SMMU, probably mostly for that reason.
I have a DT snippet for Midway, and that puts the MMIO base at ~36GB, which is not possible on Highbank.
So I think that the quirk is really meant and needed for Midway.

> > So I don't know exactly *how* desperate you are with removing this, or if
> > there are other reasons than "negative diffstat", but if possible I would
> > like to keep it in.
>
> It's more that we *do* make quite a lot of changes to the arm-smmu driver
> and it's never tested with this quirk. If you're stepping up to run smmu
> tests on my queue for each release on highbank, then great, but otherwise
> I'd rather not carry the code for fun. The change in diffstat is minimal
> (we're going to need to hooks for nvidia, who broke things in a different
> way).

I am about to set up some more sophisticated testing, and will include some SMMU bits in it.

Cheers,
Andre.

> Also, since the hooks aren't going away, if you /do/ end up using the SMMU
> in future, then we could re-add the driver quirk without any fuss.
>
> Will

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