linux-kernel - Re: [PATCH v5 2/9] iommu/arm-smmu-v3: Replace s1_cfg with cdtab

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Message-ID: <ZNTSU1Jm6OsauygC@nvidia.com>
Date:   Thu, 10 Aug 2023 09:04:35 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Will Deacon <will@...nel.org>
Cc:     Michael Shavit <mshavit@...gle.com>, iommu@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        robin.murphy@....com, nicolinc@...dia.com, jean-philippe@...aro.org
Subject: Re: [PATCH v5 2/9] iommu/arm-smmu-v3: Replace s1_cfg with cdtab_cfg

On Thu, Aug 10, 2023 at 10:43:33AM +0100, Will Deacon wrote:
> On Thu, Aug 10, 2023 at 05:33:53PM +0800, Michael Shavit wrote:
> > > > > Sounds a lot like the existing s1fmt field. Can we keep it?
> > > >
> > > > If you are OK with the dead code, I don't object. But let's put it in
> > > > the struct arm_smmu_ctx_desc_cfg.
> > >
> > > Ok, we have a deal!
> > 
> > What dead code? Is the deal here that we keep the field, but still
> > infer the value to write from (cd_table->l1_desc == null) in
> > arm_smmu_write_strtab_ent??
> 
> Keep the field and write it directly when populating the ste (i.e. don't
> infer anything), but the field moves into 'struct arm_smmu_ctx_desc_cfg'.

Yes - the 'dead code' is that we introduce storage for a field that is
always a known constant (STRTAB_STE_0_S1FMT_64K_L2).

Jason