linux-kernel - Re: [RFC,PATCH 2/3] clk: Generic support for fixed-rate clocks

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Date:	Fri, 11 Feb 2011 12:23:56 +1300
From:	Ryan Mallon <ryan@...ewatersys.com>
To:	Jeremy Kerr <jeremy.kerr@...onical.com>
CC:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-sh@...r.kernel.org,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Paul Mundt <lethal@...ux-sh.org>,
	Dima Zavin <dmitriyz@...gle.com>,
	Saravana Kannan <skannan@...eaurora.org>,
	Ben Dooks <ben-linux@...ff.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [RFC,PATCH 2/3] clk: Generic support for fixed-rate clocks

On 02/09/2011 07:41 PM, Jeremy Kerr wrote:
> Since most platforms will need a fixed-rate clock, add one. This will
> also serve as a basic example of an implementation of struct clk.
> 
> Signed-off-by: Jeremy Kerr <jeremy.kerr@...onical.com>
> 
> ---
>  drivers/clk/clk.c   |   14 ++++++++++++++
>  include/linux/clk.h |   16 ++++++++++++++++
>  2 files changed, 30 insertions(+)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index c35478a..bbbdb0d 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -124,3 +124,17 @@ void __clk_put(struct clk *clk)
>  	if (clk->ops->put)
>  		clk->ops->put(clk);
>  }
> +
> +/* clk_fixed support */
> +
> +#define to_clk_fixed(clk) (container_of(clk, struct clk_fixed, clk))
> +
> +static unsigned long clk_fixed_get_rate(struct clk *clk)
> +{
> +	return to_clk_fixed(clk)->rate;
> +}
> +
> +struct clk_ops clk_fixed_ops = {
> +	.get_rate = clk_fixed_get_rate,
> +};
> +EXPORT_SYMBOL_GPL(clk_fixed_ops);
> diff --git a/include/linux/clk.h b/include/linux/clk.h
> index fe806b7..e67fdb0 100644
> --- a/include/linux/clk.h
> +++ b/include/linux/clk.h
> @@ -185,6 +185,22 @@ static inline void clk_common_init(struct clk *clk)
>  	mutex_init(&clk->prepare_lock);
>  }
>  
> +/* Simple fixed-rate clock */
> +struct clk_fixed {
> +	struct clk	clk;
> +	unsigned long	rate;
> +};
> +
> +extern struct clk_ops clk_fixed_ops;
> +
> +#define INIT_CLK_FIXED(name, r) { \
> +	.clk = INIT_CLK(name.clk, clk_fixed_ops), \
> +	.rate = (r) \
> +}

A fixed clock may still have other operations such as enable/disable.
Maybe do something like this instead:

#define INIT_CLK_FIXED(name, ops, r) { 		\
	.clk = INIT_CLK(name.clk, ops, rate), 	\
	.clk.ops.get_rate = clk_fixed_get_rate, \
	.rate = (r),				\
}

That's untested though. I'm not sure if you can reliably assign
something twice in a struct initialiser?

~Ryan

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