linux-kernel - Re: [PATCH v3 0/7] Cavium ThunderX2 SMMUv3 errata workarounds

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Date:   Tue, 9 May 2017 18:07:29 +0200
From:   Robert Richter <robert.richter@...ium.com>
To:     Linu Cherian <linu.cherian@...ium.com>
Cc:     Geetha sowjanya <gakula@...iumnetworks.com>, will.deacon@....com,
        robin.murphy@....com, lorenzo.pieralisi@....com,
        hanjun.guo@...aro.org, sudeep.holla@....com,
        iommu@...ts.linux-foundation.org, jcm@...hat.com,
        linux-kernel@...r.kernel.org, catalin.marinas@....com,
        sgoutham@...ium.com, linux-arm-kernel@...ts.infradead.org,
        linux-acpi@...r.kernel.org, geethasowjanya.akula@...il.com,
        Charles.Garcia-Tobin@....com
Subject: Re: [PATCH v3 0/7] Cavium ThunderX2 SMMUv3 errata workarounds

On 08.05.17 20:45:36, Linu Cherian wrote:
> On Sat May 06, 2017 at 12:22:50AM +0200, Robert Richter wrote:
> > On 05.05.17 17:38:04, Geetha sowjanya wrote:
> > > From: Linu Cherian <linu.cherian@...ium.com>
> > > 
> > > Cavium ThunderX2 SMMUv3 implementation has two Silicon Erratas.
> > > 1. Errata ID #74
> > >    SMMU register alias Page 1 is not implemented
> > > 2. Errata ID #126
> > >    SMMU doesnt support unique IRQ lines and also MSI for gerror, 
> > >    eventq and cmdq-sync
> > > 
> > > The following patchset does software workaround for these two erratas.
> > > 
> > > This series is based on patchset. 
> > > https://www.spinics.net/lists/arm-kernel/msg578443.html
> > > 
> > > Changes from v1:
> > >  Since the use of MIDR register is rejected and SMMU_IIDR is broken on this 
> > >  silicon, as suggested by Will Deacon modified the patches to use ThunderX2 
> > >  SMMUv3 IORT model number to enable errata workaround.
> > > 
> > > Changes from v2:
> > >  Updated "Documentation/devicetree/bindings/iommu/arm,smmu-v3.txt" document with 
> > >  new SMMU option used to enable errata workaround.
> > >  
> > > Geetha Sowjanya (1):
> > >   iommu/arm-smmu-v3: Add workaround for Cavium ThunderX2 erratum #126
> > > 
> > > Linu Cherian (6):
> > >   iommu/arm-smmu-v3: Introduce smmu option PAGE0_REGS_ONLY for ThunderX2
> > >     errata#74.
> > >   iommu/arm-smmu-v3: Do resource size checks based on SMMU option
> > >     PAGE0_REGS_ONLY
> > >   ACPICA: IORT: Add Cavium ThunderX2 SMMUv3 model definition.
> > >   iommu/arm-smmu-v3: For ACPI based device probing, set PAGE0_REGS_ONLY
> > >     option     for ThunderX2 SMMUv3 implementations.
> > >   ACPI/IORT: Fixup SMMUv3 resource size for Cavium ThunderX2 SMMUv3
> > >     model
> > >   arm64: Documentation: Add Cavium ThunderX2 SMMUv3 erratas
> > 
> > This split into patches does not look reasonable to me. 1 patch only
> > for each workaround should be sufficient.
> > 
> 
> * Should we not atleast keep the changes in drivers/acpi/iort.c and
>  include/acpi/actbl2.h seperate, since they are outside smmuv3 driver ? 

IMO both patches depend each other. You can't shrink the io space
first without adjusting the offset when accessing it. At least the
order should be changed. But since it is one workaround I would prefer
also one patch.

-Robert