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

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Message-ID: <20200228141130.18be5bb8@donnerap.cambridge.arm.com>
Date:   Fri, 28 Feb 2020 14:11:30 +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>,
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        "David S. Miller" <davem@...emloft.net>,
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        Linux IOMMU <iommu@...ts.linux-foundation.org>,
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        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 13:56:46 +0000
Will Deacon <will@...nel.org> wrote:

> On Fri, Feb 28, 2020 at 01:42:54PM +0000, Andre Przywara wrote:
> > 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 Tue, Feb 25, 2020 at 04:01:54PM -0600, Rob Herring wrote:    
> > > > > > 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.  
> 
> Sorry, but I don't follow your reasoning here. The MMIO base has nothing
> to do with the quirk,

It hasn't, but Highbank has no LPAE, so couldn't possible have a device at such an address. And this is the only MMIO address I know of.

> although doing some digging it looks like your
> conclusion about this applying to Midway (ecx-2000?) is correct:
> 
> http://lists.infradead.org/pipermail/linux-arm-kernel/2014-January/226095.html

Right, thanks for that find. Yes, Midway is the codename for the ECX-2000 SoC product.

Cheers,
Andre
 
> > > > 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.  
> 
> Yes, please.
> 
> Will