netdev - Re: [RFC PATCH 06/11] iommu: arm-smmu: Remove Calxeda secure mode quirk

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Message-ID: <20200228134254.03fc5e1b@donnerap.cambridge.arm.com>
Date:   Fri, 28 Feb 2020 13:42:54 +0000
From:   Andre Przywara <andre.przywara@....com>
To:     Will Deacon <will@...nel.org>
Cc:     Rob Herring <robh@...nel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        soc@...nel.org, Robert Richter <rrichter@...vell.com>,
        Jon Loeliger <jdl@....com>, Alexander Graf <graf@...zon.com>,
        Matthias Brugger <mbrugger@...e.com>,
        Mark Langsdorf <mlangsdo@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Cornelia Huck <cohuck@...hat.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        "David S. Miller" <davem@...emloft.net>,
        devicetree@...r.kernel.org, Eric Auger <eric.auger@...hat.com>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        James Morse <james.morse@....com>,
        Jens Axboe <axboe@...nel.dk>, Joerg Roedel <joro@...tes.org>,
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        <linux-ide@...r.kernel.org>,
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        Robin Murphy <robin.murphy@....com>,
        Stephen Boyd <sboyd@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [RFC PATCH 06/11] iommu: arm-smmu: Remove Calxeda secure mode
 quirk

On Fri, 28 Feb 2020 10:50:25 +0000
Will Deacon <will@...nel.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@...nel.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@...nel.org> wrote:    
> > > > >
> > > > > On Tue, Feb 18, 2020 at 11:13:16AM -0600, Rob Herring wrote:    
> > > > > > Cc: Will Deacon <will@...nel.org>
> > > > > > Cc: Robin Murphy <robin.murphy@....com>
> > > > > > Cc: Joerg Roedel <joro@...tes.org>
> > > > > > Cc: iommu@...ts.linux-foundation.org
> > > > > > Signed-off-by: Rob Herring <robh@...nel.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