[PATCH 05/10] clk: Add support for simple dividers

[Richard Zhao]

On Fri, Apr 15, 2011 at 09:08:10PM +0200, Sascha Hauer wrote:
> This patch adds support for the most common type of divider,
> which expects a register, width and shift values to desacribe
> the location of the divider. The divider can be zero based
> or one based (div = reg_val + 1 vs. div = reg_val).
> 
> Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
> Cc: Jeremy Kerr <jeremy.kerr at canonical.com>
> ---
>  drivers/clk/Kconfig       |    3 +
>  drivers/clk/Makefile      |    1 +
>  drivers/clk/clk-divider.c |  132 +++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/clk.h       |   31 +++++++++++
>  4 files changed, 167 insertions(+), 0 deletions(-)
>  create mode 100644 drivers/clk/clk-divider.c
> 
> diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
> index 6e3ae54..76bb4c9 100644
> --- a/drivers/clk/Kconfig
> +++ b/drivers/clk/Kconfig
> @@ -5,3 +5,6 @@ config CLKDEV_LOOKUP
>  
>  config USE_COMMON_STRUCT_CLK
>  	bool
> +
> +config USE_COMMON_CLK_DIVIDER
> +	bool
> diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
> index a1a06d3..723d884 100644
> --- a/drivers/clk/Makefile
> +++ b/drivers/clk/Makefile
> @@ -1,3 +1,4 @@
>  
>  obj-$(CONFIG_CLKDEV_LOOKUP)	+= clkdev.o
>  obj-$(CONFIG_USE_COMMON_STRUCT_CLK) += clk.o
> +obj-$(CONFIG_USE_COMMON_CLK_DIVIDER) += clk-divider.o
> diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
> new file mode 100644
> index 0000000..2de94df
> --- /dev/null
> +++ b/drivers/clk/clk-divider.c
> @@ -0,0 +1,132 @@
> +/*
> + * Copyright (C) 2011 Sascha Hauer <s.hauer at pengutronix.de>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * Standard functionality for the common clock API.
> + */
> +#include <linux/module.h>
> +#include <linux/clk.h>
> +#include <linux/io.h>
> +
> +#define to_clk_divider(clk) (container_of(clk, struct clk_divider, clk))
> +
> +static unsigned long clk_divider_get_rate(struct clk *clk)
> +{
> +	struct clk_divider *divider = to_clk_divider(clk);
> +	unsigned long rate = clk_get_rate(divider->parent);
> +	unsigned int div;
> +
> +	div = readl(divider->reg) >> divider->shift;
> +	div &= (1 << divider->width) - 1;
> +
> +	if (!(divider->flags & CLK_DIVIDER_FLAG_ONE_BASED))
> +		div++;
> +
> +	return rate / div;
> +}
> +
> +static int clk_divider_bestdiv(struct clk *clk, unsigned long rate,
> +		unsigned long *best_parent_rate)
> +{
> +	struct clk_divider *divider = to_clk_divider(clk);
> +	int i, bestdiv = 0;
> +	unsigned long parent_rate, best = 0, now, maxdiv;
> +
> +	maxdiv = (1 << divider->width);
> +
> +	if (divider->flags & CLK_DIVIDER_FLAG_ONE_BASED)
> +		maxdiv--;
> +
> +	/*
> +	 * 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(divider->parent, (rate + 1) * i);
> +		now = parent_rate / i;
> +
> +		if (now <= rate && now >= best) {
> +			bestdiv = i;
> +			best = now;
> +		}
> +	}
> +
> +	if (!bestdiv) {
> +		bestdiv = (1 << divider->width);
> +		parent_rate = clk_round_rate(divider->parent, 1);
> +	} else {
> +		parent_rate = best * bestdiv;
> +	}
> +
> +	if (best_parent_rate)
> +		*best_parent_rate = parent_rate;
> +
> +	return bestdiv;
> +}
> +
> +static long clk_divider_round_rate(struct clk *clk, unsigned long rate)
> +{
> +	unsigned long best_parent_rate;
> +	int div = clk_divider_bestdiv(clk, rate, &best_parent_rate);
> +
> +	return best_parent_rate / div;
> +}
> +
> +static int clk_divider_set_rate(struct clk *clk, unsigned long rate)
> +{
> +	unsigned long best_parent_rate;
> +	struct clk_divider *divider = to_clk_divider(clk);
> +	unsigned int div;
> +	int ret;
> +	unsigned long flags = 0;
> +	u32 val;
> +
> +	div = clk_divider_bestdiv(clk, rate, &best_parent_rate);
> +
> +	if (rate != best_parent_rate / div)
> +		return -EINVAL;
> +
> +	ret = clk_set_rate(divider->parent, best_parent_rate);
why do you set parent rate? It may impact hte parent's other children.

Thanks
Richard
> +	if (ret)
> +		return ret;
> +
> +	if (divider->lock)
> +		spin_lock_irqsave(divider->lock, flags);
> +
> +	if (!(divider->flags & CLK_DIVIDER_FLAG_ONE_BASED))
> +		div--;
> +
> +	val = readl(divider->reg);
> +	val &= ~(((1 << divider->width) - 1) << divider->shift);
> +	val |= div << divider->shift;
> +	writel(val, divider->reg);
> +
> +	if (divider->lock)
> +		spin_unlock_irqrestore(divider->lock, flags);
> +
> +	return 0;
> +}
> +
> +static struct clk *clk_divider_get_parent(struct clk *clk)
> +{
> +	struct clk_divider *divider = to_clk_divider(clk);
> +
> +	return divider->parent;
> +}
> +
> +struct clk_ops clk_divider_ops = {
> +	.prepare = clk_parent_prepare,
> +	.unprepare = clk_parent_unprepare,
> +	.enable = clk_parent_enable,
> +	.disable = clk_parent_disable,
> +	.get_rate = clk_divider_get_rate,
> +	.round_rate = clk_divider_round_rate,
> +	.set_rate = clk_divider_set_rate,
> +	.get_parent = clk_divider_get_parent,
> +};
> +EXPORT_SYMBOL_GPL(clk_divider_ops);
> diff --git a/include/linux/clk.h b/include/linux/clk.h
> index d014341..6f9771b 100644
> --- a/include/linux/clk.h
> +++ b/include/linux/clk.h
> @@ -180,6 +180,37 @@ unsigned long clk_parent_get_rate(struct clk *clk);
>  long clk_parent_round_rate(struct clk *clk, unsigned long rate);
>  int clk_parent_set_rate(struct clk *clk, unsigned long rate);
>  
> +/**
> + * clock divider
> + *
> + * @clk		clock source
> + * @reg		register containing the divider
> + * @shift	shift to the divider
> + * @width	width of the divider
> + * @lock	register lock
> + * @parent	parent clock
> + *
> + * This clock implements get_rate/set_rate/round_rate. prepare/unprepare and
> + * enable/disable are passed through to the parent.
> + *
> + * The divider is calculated as div = reg_val + 1
> + * or if CLK_DIVIDER_FLAG_ONE_BASED is set as div = reg_val
> + * (with reg_val == 0 considered invalid)
> + */
> +struct clk_divider {
> +	struct clk	clk;
> +	void __iomem	*reg;
> +	unsigned char	shift;
> +	unsigned char	width;
> +	unsigned int	div;
> +	struct clk	*parent;
> +	spinlock_t	*lock;
> +#define CLK_DIVIDER_FLAG_ONE_BASED	(1 << 0)
> +	unsigned int	flags;
> +};
> +
> +extern struct clk_ops clk_divider_ops;
> +
>  #else /* !CONFIG_USE_COMMON_STRUCT_CLK */
>  
>  /*
> -- 
> 1.7.4.1
> 
> 
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