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Date:   Wed, 29 May 2019 21:09:17 -0700 (PDT)
Subject:     Re: [PATCH] riscv: Fix udelay in RV32.
In-Reply-To: <381ee6950c84b868ca6a3c676eb981a1980889a3.1559035050.git.nickhu@andestech.com>
CC:     greentime@andestech.com, linux-riscv@lists.infradead.org,
        linux-kernel@vger.kernel.org, nickhu@andestech.com,
        green.hu@gmail.com
From:   Palmer Dabbelt <palmer@sifive.com>
To:     nickhu@andestech.com
Message-ID: <mhng-681a0d18-f477-4e76-ae16-b64fe7265ec4@palmer-si-x1e>
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On Tue, 28 May 2019 02:26:49 PDT (-0700), nickhu@andestech.com wrote:
> In RV32, udelay would delay the wrong cycle.
> When it shifts right "UDELAY_SHITFT" bits, it
> either delays 0 cycle or 1 cycle. It only works
> correctly in RV64. Because the 'ucycles' always
> needs to be 64 bits variable.
>
> Signed-off-by: Nick Hu <nickhu@andestech.com>
> ---
>  arch/riscv/lib/delay.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/lib/delay.c b/arch/riscv/lib/delay.c
> index dce8ae24c6d3..da847f49fb74 100644
> --- a/arch/riscv/lib/delay.c
> +++ b/arch/riscv/lib/delay.c
> @@ -88,7 +88,7 @@ EXPORT_SYMBOL(__delay);
>
>  void udelay(unsigned long usecs)
>  {
> -	unsigned long ucycles = usecs * lpj_fine * UDELAY_MULT;
> +	unsigned long long ucycles = (unsigned long long)usecs * lpj_fine * UDELAY_MULT;
>
>  	if (unlikely(usecs > MAX_UDELAY_US)) {
>  		__delay((u64)usecs * riscv_timebase / 1000000ULL);

Reviewed-by: Palmer Dabbelt <palmer@sifive.com>