linux-kernel - Re: [PATCH v4 02/13] iommu/arm-smmu-v3: Add smmu_s1_cfg to smmu

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Message-ID: <CAKHBV24zQ+4waZgsYV08LzeMkjze1gTcwvEv5uL8RM1GcBgrzg@mail.gmail.com>
Date:   Mon, 17 Jul 2023 18:06:19 +0800
From:   Michael Shavit <mshavit@...gle.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Nicolin Chen <nicolinc@...dia.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>, jean-philippe@...aro.org,
        baolu.lu@...ux.intel.com, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 02/13] iommu/arm-smmu-v3: Add smmu_s1_cfg to smmu_master

On Fri, Jul 14, 2023 at 9:21 PM Jason Gunthorpe <jgg@...dia.com> wrote:
> patch 2 should delete arm_smmu_s1_cfg and just put
> arm_smmu_ctx_desc_cfg directly in the master. arm_smmu_ctx_desc_cfg is
> a weird name for the contex descriptor table, but it is much less
> weird than s1_cfg. As you say s1fmt/s1cdmax are redundant.

s1fmt is fairly trivial to replace but s1cdmax requires inversing
previous computations. I don't really buy that getting rid of it
simplifies anything, even if it's technically redundant.

> patch 3 I don't understand, we should not add something called
> s1_cfg/s2_cfg to the master. The master should have
> 'arm_smmu_ctx_desc_cfg cd_table' and 'arm_smmu_domain ste_domain'

This was simply meant to be a more convenient way of finding the
currently active cdtable from the
arm_smmu_write_ctx_desc/write_strtab_ent functions without having to
inspect the currently attached domain. But sure, that's easy enough to
revert.

> patch 5 makes sense, but something seems odd about the order as we
> somehow half moved it in patch 2?
Ack; patch 2 can be reordered to come after patch 4, or even squashed
with 5 if you prefer.

> My suggestion for patch structure is to start by cleaning up the CD
> table object. Make arm_smmu_ctx_desc_cfg the CD table, remove the
> redudencies, remove arm_s1_cfg, clean the CD table APIs to only use
> 'struct arm_smmu_ctx_desc_cfg *', add the 'ste_domain' to the master,
> and then as the last step just move the arm_smmu_ctx_desc_cfg from the
> iommu_domain to the master.
>
> And that is a nice little series on its own - you end up with a shared
> CD table in the master, and no CD table in any domains.

I don't entirely buy that refactoring s1_cfg is worth the extra
effort, nor that it should be tied to this patch series. This series
already makes s1_cfg behave as the CD table; whether we want to
entirely get rid of pre-computed data useful for writing an STE sounds
like a separate cleanup.