Re: [PATCH] riscv: delay: use do_div() instead of __udivdi3()

From: Christoph Hellwig <hch@infradead.org>
To: Paul Walmsley <paul.walmsley@sifive.com>
Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv: delay: use do_div() instead of __udivdi3()
Date: Tue, 6 Aug 2019 23:48:57 -0700	[thread overview]
Message-ID: <20190807064857.GA6942@infradead.org> (raw)
In-Reply-To: <alpine.DEB.2.21.9999.1908061906240.25231@viisi.sifive.com>

> diff --git a/arch/riscv/lib/delay.c b/arch/riscv/lib/delay.c
> index 87ff89e88f2c..8c686934e0f6 100644
> --- a/arch/riscv/lib/delay.c
> +++ b/arch/riscv/lib/delay.c
> @@ -81,9 +81,14 @@ EXPORT_SYMBOL(__delay);
>  void udelay(unsigned long usecs)
>  {
>  	u64 ucycles = (u64)usecs * lpj_fine * UDELAY_MULT;
> +	u64 n;
> +	u32 rem;
>  
>  	if (unlikely(usecs > MAX_UDELAY_US)) {
> -		__delay((u64)usecs * riscv_timebase / 1000000ULL);
> +		n = (u64)usecs * riscv_timebase;
> +		rem = do_div(n, 1000000);
> +
> +		__delay(n);
>  		return;

A few comments on the variable usage:

I think you really want a variable of type u64 that contains the usecs
value instead of casting it three times.

n and rem can be easily declared inside the branch.

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