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 12:10:32 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
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 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/

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds