linux-kernel - Re: [PATCH v2 0/2] riscv: improve unaligned memory accesses

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Date:   Fri, 17 Sep 2021 22:14:29 +0800
From:   Jisheng Zhang <jszhang3@...l.ustc.edu.cn>
To:     Chen Huang <chenhuang5@...wei.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Darius Rad <darius@...espec.com>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/2] riscv: improve unaligned memory accesses

On Thu, 16 Sep 2021 13:08:53 +0000
Chen Huang <chenhuang5@...wei.com> wrote:

> The patchset improves RISCV unaligned memory accesses, selects
> HAVE_EFFICIENT_UNALIGNED_ACCESS if CPU_HAS_NO_UNALIGNED not
> enabled and supports DCACHE_WORD_ACCESS to improve the efficiency
> of unaligned memory accesses.
> 
> If CPU don't support unaligned memory accesses for now, please
> select CONFIG_CPU_HAS_NO_UNALIGNED. For I don't know which CPU
> don't support unaligned memory accesses, I don't choose the
> CONFIG for them.

This will break unified kernel Image for riscv. Obviously, we will have
two images for efficient unaligned access platforms and non-efficient
unaligned access platforms. IMHO, we may need alternative mechanism or
something else to dynamically enable related code path.

Regards

> 
> Changes since v1:
>  - As Darius Rad and Jisheng Zhang mentioned, some CPUs don't support
>    unaligned memory accesses, add an option for CPUs to choose it or not.
> 
> Chen Huang (2):
>   riscv: support HAVE_EFFICIENT_UNALIGNED_ACCESS
>   riscv: Support DCACHE_WORD_ACCESS
> 
>  arch/riscv/Kconfig                      |  5 ++++
>  arch/riscv/include/asm/word-at-a-time.h | 37 +++++++++++++++++++++++++
>  2 files changed, 42 insertions(+)
>