linux-kernel - Re: [PATCH v5 6/6] soc: renesas: Add L2 cache management for RZ/Five SoC

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Message-Id: <bb350709-e29a-402c-8e7e-37fd9c452c6d@app.fastmail.com>
Date:   Thu, 29 Dec 2022 15:05:37 +0100
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Conor Dooley" <conor@...nel.org>
Cc:     linux-riscv@...ts.infradead.org,
        "Geert Uytterhoeven" <geert@...ux-m68k.org>, soc@...nel.org,
        Prabhakar <prabhakar.csengg@...il.com>,
        "Paul Walmsley" <paul.walmsley@...ive.com>,
        "Albert Ou" <aou@...s.berkeley.edu>,
        "Magnus Damm" <magnus.damm@...il.com>,
        Heiko Stübner <heiko@...ech.de>,
        "Conor.Dooley" <conor.dooley@...rochip.com>,
        "Samuel Holland" <samuel@...lland.org>, guoren <guoren@...nel.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        krzysztof.kozlowski+dt@...aro.org,
        "Jisheng Zhang" <jszhang@...nel.org>,
        "Atish Patra" <atishp@...osinc.com>,
        "Anup Patel" <apatel@...tanamicro.com>,
        "Andrew Jones" <ajones@...tanamicro.com>,
        "Nathan Chancellor" <nathan@...nel.org>,
        "Philipp Tomsich" <philipp.tomsich@...ll.eu>,
        devicetree@...r.kernel.org,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        linux-kernel@...r.kernel.org,
        "Biju Das" <biju.das.jz@...renesas.com>,
        "Lad, Prabhakar" <prabhakar.mahadev-lad.rj@...renesas.com>,
        "Palmer Dabbelt" <palmer@...belt.com>,
        "Christoph Hellwig" <hch@...radead.org>
Subject: Re: [PATCH v5 6/6] soc: renesas: Add L2 cache management for RZ/Five SoC

On Sat, Dec 17, 2022, at 23:52, Conor Dooley wrote:
> On Fri, Dec 16, 2022 at 09:04:20PM +0100, Arnd Bergmann wrote:
>> On Fri, Dec 16, 2022, at 17:32, Palmer Dabbelt wrote:
>> > On Thu, 15 Dec 2022 23:02:58 PST (-0800), Christoph Hellwig wrote:
>>
>> I don't particularly like drivers/soc/ to become more of a dumping
>> ground for random drivers. If there are several SoCs that have the
>> same requirement to do a particular thing, the logical step would
>> be to put them into a proper subsystem, with a well-defined interface
>> to dma-mapping and virtualization frameworks.
>> 
>> The other things we have in drivers/soc/ are usually either
>> soc_device drivers for identifying the system, or they export
>> interfaces used by soc specific drivers.
>
> Sounds like that's two "not in my back yard" votes from the maintainers
> in question..
> Doing drivers/cache would allow us to co-locate the RISC-V cache
> management bits since it is not just going to be the ax45mp l2 driver
> that will need to have them.
>
> Would it be okay to put this driver in soc/andestech for now & then move
> it, and the SiFive one, once we've got patches posted for cache
> management with that?

I actually had a look at both of these drivers now and
found that they do entirely different things, so I would
revise what I had said earlier. Sorry for not having paid
enough attention at first.

The Sifive L2 cache driver handles an interrupt from the
cache controller that is trigger by data corruption
(corectable or uncorrectable). This is used as an
implementation detail of drivers/edac/sifive_edac.c
and could probably just be merged into that file.

The Andes cache driver in this series on the other hand
does not do EDAC at all but instead handles cache maintenance
for the dma-mapping interface by hooking into the
inline-asm implementation details of arch/riscv/mm/dma-noncoherent.c
as an errata fix. If we expect more nonstandard ways
to manage cache controllers for this, I think this
needs a proper interface in arch/riscv or drivers/cache.

This could be done the same way as arch/arm/include/asm/cacheflush.h
with CPU specific cache management callback pointers, but
can't really be a separate device driver without interacting
with low-level architecture code.

     Arnd