linux-kernel - Re: [PATCH v6 3/6] riscv: errata: Add Andes alternative ports

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Message-ID: <Y7iWTwZwNLiU8USP@spud>
Date:   Fri, 6 Jan 2023 21:44:47 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Prabhakar <prabhakar.csengg@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Heiko Stuebner <heiko@...ech.de>, 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>,
        "open list:RISC-V ARCHITECTURE" <linux-riscv@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Philipp Tomsich <philipp.tomsich@...ll.eu>,
        Jisheng Zhang <jszhang@...nel.org>
Subject: Re: [PATCH v6 3/6] riscv: errata: Add Andes alternative ports

On Fri, Jan 06, 2023 at 06:55:23PM +0000, Prabhakar wrote:
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> 
> Add required ports of the Alternative scheme for Andes CPU cores.
> 
> I/O Coherence Port (IOCP) provides an AXI interface for connecting external
> non-caching masters, such as DMA controllers. IOCP is a specification
> option and is disabled on the Renesas RZ/Five SoC due to this reason cache
> management needs a software workaround.
> 
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> ---
> v5 -> v6
> * Dropped patching alternative and now just probing IOCP
> 
> v4 -> v5
> * Sorted the Kconfig/Makefile/Switch based on Core name
> * Added a comments
> * Introduced RZFIVE_SBI_EXT_IOCP_SW_WORKAROUND SBI EXT ID to check if
>   CMO needs to be applied. Is there a way we can access the DTB while patching
>   as we can drop this SBI EXT ID and add a DT property instead for cmo?
> 
> RFC v3 -> v4
> * New patch
> ---
>  arch/riscv/Kconfig.erratas           | 22 +++++++++
>  arch/riscv/errata/Makefile           |  1 +
>  arch/riscv/errata/andes/Makefile     |  1 +
>  arch/riscv/errata/andes/errata.c     | 71 ++++++++++++++++++++++++++++
>  arch/riscv/include/asm/alternative.h |  3 ++
>  arch/riscv/kernel/alternative.c      |  5 ++
>  6 files changed, 103 insertions(+)
>  create mode 100644 arch/riscv/errata/andes/Makefile
>  create mode 100644 arch/riscv/errata/andes/errata.c
> 
> diff --git a/arch/riscv/Kconfig.erratas b/arch/riscv/Kconfig.erratas
> index 69621ae6d647..f0f0c1abd52b 100644
> --- a/arch/riscv/Kconfig.erratas
> +++ b/arch/riscv/Kconfig.erratas
> @@ -1,5 +1,27 @@
>  menu "CPU errata selection"
>  
> +config ERRATA_ANDES
> +	bool "Andes AX45MP errata"
> +	depends on !XIP_KERNEL
> +	select RISCV_ALTERNATIVE
> +	help
> +	  All Andes errata Kconfig depend on this Kconfig. Disabling
> +	  this Kconfig will disable all Andes errata. Please say "Y"
> +	  here if your platform uses Andes CPU cores.
> +
> +	  Otherwise, please say "N" here to avoid unnecessary overhead.
> +
> +config ERRATA_ANDES_CMO
> +	bool "Apply Andes cache management errata"
> +	depends on ERRATA_ANDES && MMU && ARCH_R9A07G043
> +	select RISCV_DMA_NONCOHERENT
> +	default y
> +	help
> +	  This will apply the cache management errata to handle the
> +	  non-standard handling on non-coherent operations on Andes cores.
> +
> +	  If you don't know what to do here, say "Y".

Ideally we would not need errata to turn this stuff on at all, but, as
you pointed out to me off-list, arch_setup_dma_ops() complains if we
have not set up.

I'm happy to commit to trying to sort that out in follow on work w/ MPFS,
since in that case it really isn't errata, and not require it for this
series as you do fit that particular bill IMO.

Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>

Thanks,
Conor.


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