linux-kernel - Re: [PATCH 01/11] RISC-V: drivers/iommu: Add RISC-V IOMMU

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Date:   Wed, 19 Jul 2023 21:49:55 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Tomasz Jeznach <tjeznach@...osinc.com>
Cc:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Anup Patel <apatel@...tanamicro.com>,
        Albert Ou <aou@...s.berkeley.edu>, linux@...osinc.com,
        linux-kernel@...r.kernel.org, Sebastien Boeuf <seb@...osinc.com>,
        iommu@...ts.linux.dev, Palmer Dabbelt <palmer@...belt.com>,
        Nick Kossifidis <mick@....forth.gr>,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH 01/11] RISC-V: drivers/iommu: Add RISC-V IOMMU - Ziommu
 support.

Hey Tomasz,

On Wed, Jul 19, 2023 at 12:33:45PM -0700, Tomasz Jeznach wrote:
> The patch introduces skeleton IOMMU device driver implementation as defined
> by RISC-V IOMMU Architecture Specification, Version 1.0 [1], with minimal support
> for pass-through mapping, basic initialization and bindings for platform and PCIe
> hardware implementations.
> 
> Series of patches following specification evolution has been reorganized to provide
> functional separation of implemented blocks, compliant with ratified specification.
> 
> This and following patch series includes code contributed by: Nick Kossifidis
> <mick@....forth.gr> (iommu-platform device, number of specification clarification
> and bugfixes and readability improvements), Sebastien Boeuf <seb@...osinc.com> (page
> table creation, ATS/PGR flow).
> 
> Complete history can be found at the maintainer's repository branch [2].
> 
> Device driver enables RISC-V 32/64 support for memory translation for DMA capable
> PCI and platform devices, multilevel device directory table, process directory,
> shared virtual address support, wired and message signaled interrupt for translation
> I/O fault, page request interface and command processing.
> 
> Matching RISCV-V IOMMU device emulation implementation is available for QEMU project,
> along with educational device extensions for PASID ATS/PRI support [3].

This commit message reads like a cover letter IMO. At whatever point
you send a v2, could you re-write this focusing on what is done in the
patch itself?

Also, since I am not going to reply to any of these iommu driver patches
in a meaningful capacity, please run checkpatch.pl on your work. There
are well over 100 style etc complaints that it has highlighted. Sparse
has also gone a bit nuts, with many warnings along the lines of:
drivers/iommu/riscv/iommu.c:1568:29: warning: incorrect type in assignment (different base types)
drivers/iommu/riscv/iommu.c:1568:29:    expected unsigned long long [usertype] iohgatp
drivers/iommu/riscv/iommu.c:1568:29:    got restricted __le64 [usertype]

I can provide you the full list when the patchwork automation has run
through the series.

Anyway, what I wanted to ask was whether it was valid to use the IOMMU
in a system if Ziommu is not present in whatever the ISA extension
communication mechanism is? Eg, riscv,isa or the ISA string property in
the ACPI tables.

Thanks,
Conor.

> References:
>  - [1] https://github.com/riscv-non-isa/riscv-iommu
>  - [2] https://github.com/tjeznach/linux/tree/tjeznach/riscv-iommu
>  - [3] https://github.com/tjeznach/qemu/tree/tjeznach/riscv-iommu

FYI, we have the Link: tag/trailer for this.

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