linux-kernel - Re: [PATCH v10 5/6] cache: Add L2 cache management for Andes AX45MP RISC-V core

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Date:   Mon, 31 Jul 2023 12:26:58 +0100
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Emil Renner Berthing <emil.renner.berthing@...onical.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Guo Ren <guoren@...nel.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Samuel Holland <samuel@...lland.org>,
        linux-riscv@...ts.infradead.org,
        Christoph Hellwig <hch@...radead.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org,
        Biju Das <biju.das.jz@...renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v10 5/6] cache: Add L2 cache management for Andes AX45MP
 RISC-V core

Hi Emil,

Thank you for the review.

On Mon, Jul 31, 2023 at 9:53 AM Emil Renner Berthing
<emil.renner.berthing@...onical.com> wrote:
>
> On Sun, 2 Jul 2023 at 22:37, 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.
> >
<snip>
> > +static const struct riscv_cache_ops ax45mp_cmo_ops = {
> > +       .wback = &ax45mp_dma_cache_wback,
> > +       .inv = &ax45mp_dma_cache_inv,
> > +       .wback_inv = &ax45mp_dma_cache_wback_inv,
> > +};
>
> Hi Prabhakar,
>
> If you're respinning this patchset anyway, I think you can mark this
> struct as __initdata since it's only used by
> riscv_noncoherent_register_cache_ops which copies the contents.
>
Agreed, I will update it in the next version.

Cheers,
Prabhakar