Subject: [PATCH 5/5] clk: add a fixed factor clock

From: [email-masked] (Saravana Kannan)
Date: Mon, 07 May 2012 12:54:29 -0700

On 05/06/2012 10:08 PM, Mike Turquette wrote:
> From: Sascha Hauer<[email-masked]>
>
> Having fixed factors/dividers in hardware is a common pattern, so
> add a basic clock type doing this. It basically describes a fixed
> factor clock using a nominator and a denominator.
>
> Signed-off-by: Sascha Hauer<[email-masked]>
> Reviewed-by: Viresh Kumar<[email-masked]>
> [mturquette at linaro.org: constify parent_names in static init macro]
> [mturquette at linaro.org: copy/paste bug from mux in static init macro]
> [mturquette at linaro.org: fix error handling in clk_register_fixed_factor]
> Signed-off-by: Mike Turquette<[email-masked]>
> ---
>   drivers/clk/Makefile           |    2 +-
>   drivers/clk/clk-fixed-factor.c |   95 ++++++++++++++++++++++++++++++++++++++++
>   include/linux/clk-private.h    |   20 ++++++++
>   include/linux/clk-provider.h   |   23 ++++++++++
>   4 files changed, 139 insertions(+), 1 deletions(-)
>   create mode 100644 drivers/clk/clk-fixed-factor.c
>
> diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
> index 1f736bc..24aa714 100644
> --- a/drivers/clk/Makefile
> +++ b/drivers/clk/Makefile
> @@ -1,4 +1,4 @@
>
>   obj-$(CONFIG_CLKDEV_LOOKUP)	+= clkdev.o
>   obj-$(CONFIG_COMMON_CLK)	+= clk.o clk-fixed-rate.o clk-gate.o \
> -				   clk-mux.o clk-divider.o
> +				   clk-mux.o clk-divider.o clk-fixed-factor.o
> diff --git a/drivers/clk/clk-fixed-factor.c b/drivers/clk/clk-fixed-factor.c
> new file mode 100644
> index 0000000..1f2da01
> --- /dev/null
> +++ b/drivers/clk/clk-fixed-factor.c
> @@ -0,0 +1,95 @@
> +/*
> + * Copyright (C) 2011 Sascha Hauer, Pengutronix<[email-masked]>
> + *
> + * 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-provider.h>
> +#include<linux/slab.h>
> +#include<linux/err.h>
> +
> +/*
> + * DOC: basic fixed multiplier and divider clock that cannot gate
> + *
> + * Traits of this clock:
> + * prepare - clk_prepare only ensures that parents are prepared
> + * enable - clk_enable only ensures that parents are enabled
> + * rate - rate is fixed.  clk->rate = parent->rate / div * mult
> + * parent - fixed parent.  No clk_set_parent support
> + */
> +
> +#define to_clk_fixed_factor(_hw) container_of(_hw, struct clk_fixed_factor, hw)
> +
> +static unsigned long clk_factor_recalc_rate(struct clk_hw *hw,
> +		unsigned long parent_rate)
> +{
> +	struct clk_fixed_factor *fix = to_clk_fixed_factor(hw);
> +
> +	return (parent_rate / fix->div) * fix->mult;

Wouldn't multiplying and then dividing result in better accuracy? Is it 
worth doing that (since we will have to account for overflow)?

> +}
> +
> +static long clk_factor_round_rate(struct clk_hw *hw, unsigned long rate,
> +				unsigned long *prate)
> +{
> +	struct clk_fixed_factor *fix = to_clk_fixed_factor(hw);
> +
> +	if (__clk_get_flags(hw->clk)&  CLK_SET_RATE_PARENT) {
> +		unsigned long best_parent;
> +
> +		best_parent = (rate / fix->mult) * fix->div;
> +		*prate = __clk_round_rate(__clk_get_parent(hw->clk),
> +				best_parent);
> +	}
> +
> +	return (*prate / fix->div) * fix->mult;
> +}
> +
> +static int clk_factor_set_rate(struct clk_hw *hw, unsigned long rate,
> +				unsigned long parent_rate)
> +{
> +	return 0;
> +}
> +
> +struct clk_ops clk_fixed_factor_ops = {
> +	.round_rate = clk_factor_round_rate,
> +	.set_rate = clk_factor_set_rate,
> +	.recalc_rate = clk_factor_recalc_rate,
> +};
> +EXPORT_SYMBOL_GPL(clk_fixed_factor_ops);
> +
> +struct clk *clk_register_fixed_factor(struct device *dev, const char *name,
> +		const char *parent_name, unsigned long flags,
> +		unsigned int mult, unsigned int div)
> +{
> +	struct clk_fixed_factor *fix;
> +	struct clk_init_data init;
> +	struct clk *clk;
> +
> +	fix = kmalloc(sizeof(*fix), GFP_KERNEL);
> +	if (!fix) {
> +		pr_err("%s: could not allocate fixed factor clk\n", __func__);
> +		return ERR_PTR(-ENOMEM);
> +	}

Can we add a check for mult <= div? It doesn't look like this clock is 
meant to capture clock multipliers (if there is even anything like that 
other than PLLs).

> +
> +	/* struct clk_fixed_factor assignments */
> +	fix->mult = mult;
> +	fix->div = div;
> +	fix->hw.init =&init;
> +
> +	init.name = name;
> +	init.ops =&clk_fixed_factor_ops;
> +	init.flags = flags;
> +	init.parent_names =&parent_name;
> +	init.num_parents = 1;
> +
> +	clk = clk_register(dev,&fix->hw);
> +
> +	if (IS_ERR(clk))
> +		kfree(fix);
> +
> +	return clk;
> +}
> diff --git a/include/linux/clk-private.h b/include/linux/clk-private.h
> index b258532..eb3f84b 100644
> --- a/include/linux/clk-private.h
> +++ b/include/linux/clk-private.h
> @@ -143,6 +143,26 @@ struct clk {
>   	DEFINE_CLK(_name, clk_mux_ops, _flags, _parent_names,	\
>   			_parents);
>
> +#define DEFINE_CLK_FIXED_FACTOR(_name, _parent_name,		\
> +				_parent_ptr, _flags,		\
> +				_mult, _div)			\
> +	static struct clk _name;				\
> +	static const char *_name##_parent_names[] = {		\
> +		_parent_name,					\
> +	};							\
> +	static struct clk *_name##_parents[] = {		\
> +		_parent_ptr,					\
> +	};							\
> +	static struct clk_fixed_factor _name##_hw = {		\
> +		.hw = {						\
> +			.clk =&_name,				\
> +		},						\
> +		.mult = _mult,					\
> +		.div = _div,					\
> +	};							\
> +	DEFINE_CLK(_name, clk_fixed_factor_ops, _flags,		\
> +			_name##_parent_names, _name##_parents);
> +

I would prefer not defining a macro for this. But if we are going to do 
it, can we please at least stop doing nested macros here? It would be 
much easier for a new comer to read if we don't nest these clock macros.

Also, should we stop adding support for fully static allocation for new 
clock types? Since it's supposed to be going away soon. Since Mike 
didn't add this clock type, I'm guessing he doesn't need the clock type 
now and hence doesn't need static allocation support for it.

>   /**
>    * __clk_init - initialize the data structures in a struct clk
>    * @dev:	device initializing this clk, placeholder for now
> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> index 5db3412..c1c23b9 100644
> --- a/include/linux/clk-provider.h
> +++ b/include/linux/clk-provider.h
> @@ -277,6 +277,29 @@ struct clk *clk_register_mux(struct device *dev, const char *name,
>   		u8 clk_mux_flags, spinlock_t *lock);
>
>   /**
> + * struct clk_fixed_factor - fixed multiplier and divider clock
> + *
> + * @hw:		handle between common and hardware-specific interfaces
> + * @mult:	multiplier
> + * @div:	divider
> + *
> + * Clock with a fixed multiplier and divider. The output frequency is the
> + * parent clock rate divided by div and multiplied by mult.
> + * Implements .recalc_rate, .set_rate and .round_rate
> + */
> +
> +struct clk_fixed_factor {
> +	struct clk_hw	hw;
> +	unsigned int	mult;
> +	unsigned int	div;
> +};
> +
> +extern struct clk_ops clk_fixed_factor_ops;
> +struct clk *clk_register_fixed_factor(struct device *dev, const char *name,
> +		const char *parent_name, unsigned long flags,
> +		unsigned int mult, unsigned int div);

Should we have one header file for each common clock type? We seem to be 
adding a lot of those (which is good), but it almost feels like 
clock-provider get out of hand soon.

Thanks,
Saravana

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