linux-kernel - Re: [PATCH v7 3/3] clk: basic clock hardware types

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Date:	Fri, 16 Mar 2012 20:25:45 +0800
From:	Richard Zhao <richard.zhao@...aro.org>
To:	Mike Turquette <mturquette@...aro.org>
Cc:	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-dev@...ts.linaro.org, patches@...aro.org,
	Mike Turquette <mturquette@...com>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnd Bergman <arnd.bergmann@...aro.org>,
	Paul Walmsley <paul@...an.com>,
	Shawn Guo <shawn.guo@...escale.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Jamie Iles <jamie@...ieiles.com>,
	Saravana Kannan <skannan@...eaurora.org>,
	Magnus Damm <magnus.damm@...il.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Amit Kucheria <amit.kucheria@...aro.org>,
	Deepak Saxena <dsaxena@...aro.org>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: Re: [PATCH v7 3/3] clk: basic clock hardware types

[...]
> +static int clk_divider_bestdiv(struct clk_hw *hw, unsigned long rate,
> +		unsigned long *best_parent_rate)
> +{
> +	struct clk_divider *divider = to_clk_divider(hw);
> +	int i, bestdiv = 0;
> +	unsigned long parent_rate, best = 0, now, maxdiv;
> +
> +	if (!rate)
> +		rate = 1;
> +
> +	maxdiv = (1 << divider->width);
> +
> +	if (divider->flags & CLK_DIVIDER_ONE_BASED)
> +		maxdiv--;
> +
> +	if (!best_parent_rate) {
> +		parent_rate = __clk_get_rate(__clk_get_parent(hw->clk));
> +		bestdiv = DIV_ROUND_UP(parent_rate, rate);
> +		bestdiv = bestdiv == 0 ? 1 : bestdiv;
> +		bestdiv = bestdiv > maxdiv ? maxdiv : bestdiv;
> +		return bestdiv;
> +	}
> +
> +	/*
> +	 * The maximum divider we can use without overflowing
> +	 * unsigned long in rate * i below
> +	 */
> +	maxdiv = min(ULONG_MAX / rate, maxdiv);
> +
> +	for (i = 1; i <= maxdiv; i++) {
> +		parent_rate = __clk_round_rate(__clk_get_parent(hw->clk),
> +				MULT_ROUND_UP(rate, i));
> +		now = parent_rate / i;
> +		if (now <= rate && now > best) {
> +			bestdiv = i;
> +			best = now;
> +			*best_parent_rate = parent_rate;
Better add		if (now == rate)
				break;
There may be more than one hit for (now == rate). We'd better select
smallest div, thus smallest parent_rate.

It's the same comment for v6, but not show stopper.

Thanks
Richard
> +		}
> +	}
> +
> +	if (!bestdiv) {
> +		bestdiv = (1 << divider->width);
> +		if (divider->flags & CLK_DIVIDER_ONE_BASED)
> +			bestdiv--;
> +		*best_parent_rate = __clk_round_rate(__clk_get_parent(hw->clk), 1);
> +	}
> +
> +	return bestdiv;
> +}
 
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