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From:   "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
Date:   Wed, 5 Oct 2022 13:53:44 +0100
Message-ID: <CA+V-a8smkDmQbz76sTA5XfUm7bkY4Ee-L5xYW+-xRWkE1TYiAw@mail.gmail.com>
Subject: Re: [RFC PATCH v2 2/2] soc: renesas: Add L2 cache management for
 RZ/Five SoC
To:     Guo Ren <guoren@kernel.org>
Cc:     Geert Uytterhoeven <geert+renesas@glider.be>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Magnus Damm <magnus.damm@gmail.com>,
        Heiko Stuebner <heiko@sntech.de>,
        Conor Dooley <conor.dooley@microchip.com>,
        Philipp Tomsich <philipp.tomsich@vrull.eu>,
        Nathan Chancellor <nathan@kernel.org>,
        Atish Patra <atishp@rivosinc.com>,
        Anup Patel <apatel@ventanamicro.com>,
        linux-renesas-soc@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
        Biju Das <biju.das.jz@bp.renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
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Hi Guo,

On Wed, Oct 5, 2022 at 2:29 AM Guo Ren <guoren@kernel.org> wrote:
>
> On Tue, Oct 4, 2022 at 6:32 AM Prabhakar <prabhakar.csengg@gmail.com> wrote:
> >
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.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