Re: [PATCH V11 03/17] riscv: Use Zicbop in arch_xchg when available

[Andrew Jones <ajones@ventanamicro.com>]

On Sun, Sep 10, 2023 at 04:28:57AM -0400, guoren@kernel.org wrote:
> From: Guo Ren <guoren@linux.alibaba.com>
> 
> Cache-block prefetch instructions are HINTs to the hardware to
> indicate that software intends to perform a particular type of
> memory access in the near future. Enable ARCH_HAS_PREFETCHW and
> improve the arch_xchg for qspinlock xchg_tail.
> 
> Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@kernel.org>
> ---
>  arch/riscv/Kconfig                 | 15 +++++++++++++++
>  arch/riscv/include/asm/cmpxchg.h   |  4 +++-
>  arch/riscv/include/asm/hwcap.h     |  1 +
>  arch/riscv/include/asm/insn-def.h  |  5 +++++
>  arch/riscv/include/asm/processor.h | 13 +++++++++++++
>  arch/riscv/kernel/cpufeature.c     |  1 +
>  6 files changed, 38 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index e9ae6fa232c3..2c346fe169c1 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -617,6 +617,21 @@ config RISCV_ISA_ZICBOZ
>  
>  	   If you don't know what to do here, say Y.
>  
> +config RISCV_ISA_ZICBOP

Even if we're not concerned with looping over blocks yet, I think we
should introduce zicbop block size DT parsing at the same time we bring
zicbop support to the kernel (it's just more copy+paste from zicbom and
zicboz). It's a bit annoying that the CMO spec doesn't state that block
sizes should be the same for m/z/p. And, the fact that m/z/p are all
separate extensions leads us to needing to parse block sizes for all
three, despite the fact that in practice they'll probably be the same.

Thanks,
drew