linux-kernel - Re: [PATCH v6 3/4] riscv: Add support for non-coherent devices using zicbom extension

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Date:   Thu, 07 Jul 2022 01:02:36 +0200
From:   Heiko Stübner <heiko@...ech.de>
To:     Guo Ren <guoren@...nel.org>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Wei Fu <wefu@...hat.com>,
        Christoph Muellner <cmuellner@...ux.com>,
        Philipp Tomsich <philipp.tomsich@...ll.eu>,
        Christoph Hellwig <hch@....de>,
        Samuel Holland <samuel@...lland.org>,
        Atish Patra <atishp@...shpatra.org>,
        Anup Patel <anup@...infault.org>,
        Nick Kossifidis <mick@....forth.gr>,
        Rob Herring <robh+dt@...nel.org>, krzk+dt@...nel.org,
        devicetree <devicetree@...r.kernel.org>,
        Drew Fustini <drew@...gleboard.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Atish Patra <atish.patra@....com>
Subject: Re: [PATCH v6 3/4] riscv: Add support for non-coherent devices using zicbom extension

Hi Guo,

Am Mittwoch, 6. Juli 2022, 01:32:12 CEST schrieb Guo Ren:
> On Wed, Jul 6, 2022 at 6:47 AM Heiko Stuebner <heiko@...ech.de> wrote:
> >
> > The Zicbom ISA-extension was ratified in november 2021
> > and introduces instructions for dcache invalidate, clean
> > and flush operations.
> >
> > Implement cache management operations for non-coherent devices
> > based on them.
> >
> > Of course not all cores will support this, so implement an
> > alternative-based mechanism that replaces empty instructions
> > with ones done around Zicbom instructions.
> >
> > As discussed in previous versions, assume the platform
> > being coherent by default so that non-coherent devices need
> > to get marked accordingly by firmware.
> >
> > Reviewed-by: Christoph Hellwig <hch@....de>
> > Signed-off-by: Heiko Stuebner <heiko@...ech.de>
> > Cc: Christoph Hellwig <hch@....de>
> > Cc: Atish Patra <atish.patra@....com>
> > Cc: Guo Ren <guoren@...nel.org>
> > Cc: Anup Patel <anup@...infault.org>
> > ---
> >  arch/riscv/Kconfig                   |  31 ++++++++
> >  arch/riscv/Makefile                  |   4 +
> >  arch/riscv/include/asm/cache.h       |   4 +
> >  arch/riscv/include/asm/cacheflush.h  |  10 +++
> >  arch/riscv/include/asm/errata_list.h |  19 ++++-
> >  arch/riscv/include/asm/hwcap.h       |   1 +
> >  arch/riscv/kernel/cpu.c              |   1 +
> >  arch/riscv/kernel/cpufeature.c       |  24 ++++++
> >  arch/riscv/kernel/setup.c            |   2 +
> >  arch/riscv/mm/Makefile               |   1 +
> >  arch/riscv/mm/dma-noncoherent.c      | 112 +++++++++++++++++++++++++++
> >  11 files changed, 208 insertions(+), 1 deletion(-)
> >  create mode 100644 arch/riscv/mm/dma-noncoherent.c
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index 32ffef9f6e5b..f7b2b3a4b7f1 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -113,6 +113,7 @@ config RISCV
> >         select MODULES_USE_ELF_RELA if MODULES
> >         select MODULE_SECTIONS if MODULES
> >         select OF
> > +       select OF_DMA_DEFAULT_COHERENT
> >         select OF_EARLY_FLATTREE
> >         select OF_IRQ
> >         select PCI_DOMAINS_GENERIC if PCI
> > @@ -218,6 +219,14 @@ config PGTABLE_LEVELS
> >  config LOCKDEP_SUPPORT
> >         def_bool y
> >
> > +config RISCV_DMA_NONCOHERENT
> > +       bool
> > +       select ARCH_HAS_DMA_PREP_COHERENT
> > +       select ARCH_HAS_SYNC_DMA_FOR_DEVICE
> > +       select ARCH_HAS_SYNC_DMA_FOR_CPU
> > +       select ARCH_HAS_SETUP_DMA_OPS
> > +       select DMA_DIRECT_REMAP
> > +
> >  source "arch/riscv/Kconfig.socs"
> >  source "arch/riscv/Kconfig.erratas"
> >
> > @@ -376,6 +385,28 @@ config RISCV_ISA_SVPBMT
> >
> >            If you don't know what to do here, say Y.
> >
> > +config CC_HAS_ZICBOM
> > +       bool
> > +       default y if 64BIT && $(cc-option,-mabi=lp64 -march=rv64ima_zicbom)
> > +       default y if 32BIT && $(cc-option,-mabi=lp64 -march=rv32ima_zicbom)
>
> -mabi=lp64 for rv32?

Thanks for catching that! :-) 

When I converted over to using the real instructions for Zicbom instead of
pre-coded ones, I used a different format first for detecting the Zicbom
existence and I guess when moving over to the above I made a mistake
in the conversion.

In any case, that should of course be ilp32, same as in the Makefile.
With updated opensbi and Qemu I have now re-tested all possible
combinations and am pretty hopefully that this should fit now.

v7 following shortly.

Thanks
Heiko