linux-kernel - Re: [PATCH] riscv: Fix udelay in RV32.

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Date:   Wed, 29 May 2019 21:09:17 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     nickhu@...estech.com
CC:     greentime@...estech.com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, nickhu@...estech.com,
        green.hu@...il.com
Subject:     Re: [PATCH] riscv: Fix udelay in RV32.

On Tue, 28 May 2019 02:26:49 PDT (-0700), nickhu@...estech.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@...estech.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@...ive.com>