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Date:   Mon, 20 Jul 2020 18:17:44 -0700 (PDT)
Subject:     Re: [PATCH 1/1] riscv: Enable ARCH_HAS_FAST_MULTIPLIER for RV64I
In-Reply-To: <20200709051922.13110-1-maochenxi@eswin.com>
CC:     Paul Walmsley <paul.walmsley@sifive.com>, aou@eecs.berkeley.edu,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        chenxi.mao2013@gmail.com, maochenxi@eswin.com
From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     maochenxi@eswin.com
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On Wed, 08 Jul 2020 22:19:22 PDT (-0700), maochenxi@eswin.com wrote:
> Enable ARCH_HAS_FAST_MULTIPLIER on RV64I
> which works fine on GCC-9.3 and GCC-10.1
>
> PS2: remove ARCH_SUPPORTS_INT128 because of RV64I already enabled.
>
> Signed-off-by: Chenxi Mao <maochenxi@eswin.com>
> ---
>  arch/riscv/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 128192e14ff2..84e6777fecad 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -202,6 +202,7 @@ config ARCH_RV64I
>  	bool "RV64I"
>  	select 64BIT
>  	select ARCH_SUPPORTS_INT128 if CC_HAS_INT128 && GCC_VERSION >= 50000
> +	select ARCH_HAS_FAST_MULTIPLIER
>  	select HAVE_DYNAMIC_FTRACE if MMU
>  	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
>  	select HAVE_FTRACE_MCOUNT_RECORD

Ah, thanks -- this one didn't show up when I was looking at the last one.  I
think we can put the fast multiplier on rv32 and rv64, there shouldn't be any
difference there.  I guess in theory we should be sticking this all in some
sort of "platform type" optimization flags, but that's probably bit much for
now.