linux-kernel - Re: [PATCH v10 3/6] riscv: mm: dma-noncoherent: nonstandard cache operations support

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Date:   Fri, 28 Jul 2023 21:13:17 +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 3/6] riscv: mm: dma-noncoherent: nonstandard cache
 operations support

Hi Emil,

Thank you for the review.

On Mon, Jul 24, 2023 at 11:18 AM Emil Renner Berthing
<emil.renner.berthing@...onical.com> wrote:
>
> On Sun, 2 Jul 2023 at 22:36, Prabhakar <prabhakar.csengg@...il.com> wrote:
> >
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >
> > Introduce support for nonstandard noncoherent systems in the RISC-V
> > architecture. It enables function pointer support to handle cache
> > management in such systems.
> >
> > This patch adds a new configuration option called
> > "RISCV_NONSTANDARD_CACHE_OPS." This option is a boolean flag that
> > depends on "RISCV_DMA_NONCOHERENT" and enables the function pointer
> > support for cache management in nonstandard noncoherent systems.
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
> > Tested-by: Conor Dooley <conor.dooley@...rochip.com> # tyre-kicking on a d1
> > ---
> > v9 -> v10
> > * Added __ro_after_init compiler attribute for noncoherent_cache_ops
> > * Renamed clean -> wback
> > * Renamed inval -> inv
> > * Renamed flush -> wback_inv
> >
> > v8 -> v9
> > * New patch
> > ---
> >  arch/riscv/Kconfig                       |  7 ++++
> >  arch/riscv/include/asm/dma-noncoherent.h | 28 +++++++++++++++
> >  arch/riscv/mm/dma-noncoherent.c          | 43 ++++++++++++++++++++++++
> >  arch/riscv/mm/pmem.c                     | 13 +++++++
> >  4 files changed, 91 insertions(+)
> >  create mode 100644 arch/riscv/include/asm/dma-noncoherent.h
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index d9e451ac862a..42c86b13c5e1 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -265,6 +265,13 @@ config RISCV_DMA_NONCOHERENT
> >         select ARCH_HAS_SYNC_DMA_FOR_DEVICE
> >         select DMA_DIRECT_REMAP
> >
> > +config RISCV_NONSTANDARD_CACHE_OPS
> > +       bool
> > +       depends on RISCV_DMA_NONCOHERENT
> > +       help
> > +         This enables function pointer support for non-standard noncoherent
> > +         systems to handle cache management.
> > +
> >  config AS_HAS_INSN
> >         def_bool $(as-instr,.insn r 51$(comma) 0$(comma) 0$(comma) t0$(comma) t0$(comma) zero)
> >
> > diff --git a/arch/riscv/include/asm/dma-noncoherent.h b/arch/riscv/include/asm/dma-noncoherent.h
> > new file mode 100644
> > index 000000000000..969cf1f1363a
> > --- /dev/null
> > +++ b/arch/riscv/include/asm/dma-noncoherent.h
> > @@ -0,0 +1,28 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * Copyright (C) 2023 Renesas Electronics Corp.
> > + */
> > +
> > +#ifndef __ASM_DMA_NONCOHERENT_H
> > +#define __ASM_DMA_NONCOHERENT_H
> > +
> > +#include <linux/dma-direct.h>
> > +
> > +/*
> > + * struct riscv_cache_ops - Structure for CMO function pointers
> > + *
> > + * @wback: Function pointer for cache writeback
> > + * @inv: Function pointer for invalidating cache
> > + * @wback_inv: Function pointer for flushing the cache (writeback + invalidating)
> > + */
> > +struct riscv_cache_ops {
> > +       void (*wback)(phys_addr_t paddr, unsigned long size);
> > +       void (*inv)(phys_addr_t paddr, unsigned long size);
> > +       void (*wback_inv)(phys_addr_t paddr, unsigned long size);
>
> Hi Prabhakar
>
> Just a quick question. After Arnd's patchset the
> arch_dma_cache{inv,wback,wback_inv} functions take a phys_addr_t and
> size_t, but here you want these callbacks to take a phys_addr_t and
> unsigned long instead. Why not keep them using size_t?
>
Agreed, I will update it to use size_t instead.

Cheers,
Prabhakar