linux-kernel - Re: [PATCH v2 4/4] clk: at91: optimization of the determine

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Date:	Wed, 05 Feb 2014 09:54:42 +0100
From:	Boris BREZILLON <b.brezillon@...rkiz.com>
To:	Jean-Jacques Hiblot <jjhiblot@...phandler.com>,
	nicolas.ferre@...el.com, mturquette@...aro.org
CC:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	jason@...edaemon.net
Subject: Re: [PATCH v2 4/4] clk: at91: optimization of the determine_rate
 callback

Hi JJ,

I guess you're commit message is wrong: you're optimizing set_rate not 
determine_rate.

Best Regards,

Boris

On 05/02/2014 09:37, Jean-Jacques Hiblot wrote:
> Signed-off-by: Boris BREZILLON <b.brezillon@...rkiz.com>
> Signed-off-by: Jean-Jacques Hiblot <jjhiblot@...phandler.com>
> ---
>   drivers/clk/at91/clk-programmable.c | 38 ++++++++-----------------------------
>   1 file changed, 8 insertions(+), 30 deletions(-)
>
> diff --git a/drivers/clk/at91/clk-programmable.c b/drivers/clk/at91/clk-programmable.c
> index 7bcc725..62e2509 100644
> --- a/drivers/clk/at91/clk-programmable.c
> +++ b/drivers/clk/at91/clk-programmable.c
> @@ -139,43 +139,21 @@ static int clk_programmable_set_rate(struct clk_hw *hw, unsigned long rate,
>   	struct clk_programmable *prog = to_clk_programmable(hw);
>   	struct at91_pmc *pmc = prog->pmc;
>   	const struct clk_programmable_layout *layout = prog->layout;
> -	unsigned long best_rate = parent_rate;
> -	unsigned long best_diff;
> -	unsigned long new_diff;
> -	unsigned long cur_rate;
> +	unsigned long div = parent_rate / rate;
>   	int shift = 0;
>   	u32 tmp = pmc_read(pmc, AT91_PMC_PCKR(prog->id)) &
>   		  ~(PROG_PRES_MASK << layout->pres_shift);
>   
> -	if (rate > parent_rate)
> -		return parent_rate;
> -	else
> -		best_diff = parent_rate - rate;
> +	if (!div)
> +		return -EINVAL;
>   
> -	if (!best_diff) {
> -		pmc_write(pmc, AT91_PMC_PCKR(prog->id), tmp | shift);
> -		return 0;
> -	}
> -
> -	for (shift = 1; shift < PROG_PRES_MASK; shift++) {
> -		cur_rate = parent_rate >> shift;
> -
> -		if (cur_rate > rate)
> -			new_diff = cur_rate - rate;
> -		else
> -			new_diff = rate - cur_rate;
> -
> -		if (!new_diff)
> -			break;
> +	shift = fls(div) - 1;
>   
> -		if (new_diff < best_diff) {
> -			best_diff = new_diff;
> -			best_rate = cur_rate;
> -		}
> +	if (div != (1<<shift))
> +		return -EINVAL;
>   
> -		if (rate > cur_rate)
> -			break;
> -	}
> +	if (shift >= PROG_PRES_MASK)
> +		return -EINVAL;
>   
>   	pmc_write(pmc, AT91_PMC_PCKR(prog->id),
>   		  tmp | (shift << layout->pres_shift));

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