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

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Date:   Thu, 15 Dec 2022 17:46:42 +0000
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Magnus Damm <magnus.damm@...il.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Samuel Holland <samuel@...lland.org>,
        Guo Ren <guoren@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <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-riscv@...ts.infradead.org,
        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>
Subject: Re: [PATCH v5 6/6] soc: renesas: Add L2 cache management for RZ/Five SoC

Hi Geert,

On Thu, Dec 15, 2022 at 11:10 AM Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
>
> Hi Prabhakar,
>
> On Thu, Dec 15, 2022 at 12:06 PM Lad, Prabhakar
> <prabhakar.csengg@...il.com> wrote:
> > On Thu, Dec 15, 2022 at 10:36 AM Geert Uytterhoeven
> > <geert@...ux-m68k.org> wrote:
> > > On Mon, Dec 12, 2022 at 12:58 PM Prabhakar <prabhakar.csengg@...il.com> wrote:
> > > > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > > >
> > > > I/O Coherence Port (IOCP) provides an AXI interface for connecting
> > > > external non-caching masters, such as DMA controllers. The accesses
> > > > from IOCP are coherent with D-Caches and L2 Cache.
> > > >
> > > > IOCP is a specification option and is disabled on the Renesas RZ/Five
> > > > SoC due to this reason IP blocks using DMA will fail.
> > > >
> > > > 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
> > > >
> > > > More info about PMA (section 10.3):
> > > > Link: http://www.andestech.com/wp-content/uploads/AX45MP-1C-Rev.-5.0.0-Datasheet.pdf
> > > >
> > > > As a workaround for SoCs with IOCP disabled CMO needs to be handled by
> > > > software. Firstly OpenSBI configures the memory region as
> > > > "Memory, Non-cacheable, Bufferable" and passes this region as a global
> > > > shared dma pool as a DT node. With DMA_GLOBAL_POOL enabled all DMA
> > > > allocations happen from this region and synchronization callbacks are
> > > > implemented to synchronize when doing DMA transactions.
> > > >
> > > > Example PMA region passes as a DT node from OpenSBI:
> > > >     reserved-memory {
> > > >         #address-cells = <2>;
> > > >         #size-cells = <2>;
> > > >         ranges;
> > > >
> > > >         pma_resv0@...00000 {
> > > >             compatible = "shared-dma-pool";
> > > >             reg = <0x0 0x58000000 0x0 0x08000000>;
> > > >             no-map;
> > > >             linux,dma-default;
> > > >         };
> > > >     };
> > > >
> > > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > >
> > > Thanks for your patch!
> > >
> > > >  arch/riscv/include/asm/cacheflush.h       |   8 +
> > > >  arch/riscv/include/asm/errata_list.h      |  28 ++-
> > > >  drivers/soc/renesas/Kconfig               |   6 +
> > > >  drivers/soc/renesas/Makefile              |   2 +
> > > >  drivers/soc/renesas/rzfive/Kconfig        |   6 +
> > > >  drivers/soc/renesas/rzfive/Makefile       |   3 +
> > > >  drivers/soc/renesas/rzfive/ax45mp_cache.c | 256 ++++++++++++++++++++++
> > >
> > > Given this touches arch/riscv/include/asm/, I don't think the
> > > code belongs under drivers/soc/renesas/.
> > >
> > Ok. Do you have any suggestions on where you want me to put this code?
>
> As it plugs into core riscv functionality, I think it should be under
> arch/riscv/.
> if the RISC-V maintainers object to that, another option is
> drivers/soc/andestech/ or (new) drivers/cache/
>
RISC-V maintainers had already made it clear to not to include vendor
specific stuff in the arch/riscv folder, so I'll consider putting this
into drivers/cache/ folder to sync with the bindings.

Conor/Palmer - do you have any objections/suggestions?

Cheers,
Prabhakar