linux-kernel - Re: [RFC PATCH v2 2/2] soc: renesas: Add L2 cache management for RZ/Five SoC

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Date:   Wed, 5 Oct 2022 13:53:44 +0100
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Guo Ren <guoren@...nel.org>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Magnus Damm <magnus.damm@...il.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Philipp Tomsich <philipp.tomsich@...ll.eu>,
        Nathan Chancellor <nathan@...nel.org>,
        Atish Patra <atishp@...osinc.com>,
        Anup Patel <apatel@...tanamicro.com>,
        linux-renesas-soc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        Biju Das <biju.das.jz@...renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [RFC PATCH v2 2/2] soc: renesas: Add L2 cache management for
 RZ/Five SoC

Hi Guo,

On Wed, Oct 5, 2022 at 2:29 AM Guo Ren <guoren@...nel.org> wrote:
>
> On Tue, Oct 4, 2022 at 6:32 AM Prabhakar <prabhakar.csengg@...il.com> wrote:
> >
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >
> > On the AX45MP core, cache coherency is a specification option so it may
> > not be supported. In this case DMA will fail. As a workaround, firstly we
> > allocate a global dma coherent pool from which DMA allocations are taken
> > and marked as non-cacheable + bufferable using the PMA region as specified
> > in the device tree. Synchronization callbacks are implemented to
> > synchronize when doing DMA transactions.
> >
> > The Andes AX45MP core has a Programmable Physical Memory Attributes (PMA)
> > block that allows dynamic adjustment of memory attributes in the runtime.
> > It contains a configurable amount of PMA entries implemented as CSR
> > registers to control the attributes of memory locations in interest.
> >
> > Below are the memory attributes supported:
> > * Device, Non-bufferable
> > * Device, bufferable
> > * Memory, Non-cacheable, Non-bufferable
> > * Memory, Non-cacheable, Bufferable
> > * Memory, Write-back, No-allocate
> > * Memory, Write-back, Read-allocate
> > * Memory, Write-back, Write-allocate
> > * Memory, Write-back, Read and Write-allocate
> Seems Svpbmt's PMA, IO, and NC wouldn't fit your requirements, could
> give a map list of the types of Svpbmt? And give out what you needed,
> but Svpbmt can't.
>
Sorry I didn't get what you meant here, could you please elaborate.

> Here is the Linux dma type to Svpbmt map:
> PMA -> Normal
> IO -> ioremap, pgprot_noncached
> NC -> pgprot_writecombine
>
> How about AX45MP?
>
Svpbmt extension is not supported on AX45MP (reported by
riscv_isa_extension_available())

Cheers,
Prabhakar