Subject: Re: [RFC,PATCH 1/7 v2] Add a common struct clk

From: Ben Dooks <[email-masked]>
Date: Tue, 12 Jan 2010 14:30:19 +0000

On Tue, Jan 12, 2010 at 05:58:31PM +1100, Jeremy Kerr wrote:
> We currently have 21 definitions of struct clk in the ARM architecture,
> each defined on a per-platform basis. This makes it difficult to define
> platform- (or architecture-) independent clock sources without making
> assumptions about struct clk.
> 
> This change is an effort to unify struct clk where possible, by defining
> a common struct clk, containing a set of clock operations. Different
> clock implementations can set their own operations, and have a standard
> interface for generic code. The callback interface is exposed to the
> kernel proper, while the clock implementations only need to be seen by
> the platform internals.
> 
> This allows us to share clock code among platforms, and makes it
> possible to dynamically create clock devices in platform-independent
> code.
> 
> Platforms can enable the generic struct clock through
> CONFIG_USE_COMMON_STRUCT_CLK.
> 
> The common clock definitions are based on a development patch from Ben
> Herrenschmidt <[email-masked]>.
> 
> Signed-off-by: Jeremy Kerr <[email-masked]>
> 
> ---
>  arch/Kconfig        |    3 
>  include/linux/clk.h |  134 +++++++++++++++++++++++++++++++++++---------
>  2 files changed, 110 insertions(+), 27 deletions(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 9d055b4..cefc026 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -140,4 +140,7 @@ config HAVE_HW_BREAKPOINT
>  config HAVE_USER_RETURN_NOTIFIER
>  	bool
>  
> +config USE_COMMON_STRUCT_CLK
> +	bool
> +
>  source "kernel/gcov/Kconfig"
> diff --git a/include/linux/clk.h b/include/linux/clk.h
> index 1d37f42..1a6199e 100644
> --- a/include/linux/clk.h
> +++ b/include/linux/clk.h
> @@ -11,36 +11,101 @@
>  #ifndef __LINUX_CLK_H
>  #define __LINUX_CLK_H
>  
> -struct device;
> +#include <linux/err.h>
>  
> -/*
> - * The base API.
> +#ifdef CONFIG_USE_COMMON_STRUCT_CLK
> +
> +/* If we're using the common struct clk, we define the base clk object here,
> + * which will be 'subclassed' by device-specific implementations. For example:
> + *
> + *  struct clk_foo {
> + *      struct clk;
> + *      [device specific fields]
> + *  };
> + *
> + * We define the common clock API through a set of static inlines that call the
> + * corresponding clk_operations. The API is exactly the same as that documented
> + * in the !CONFIG_USE_COMMON_STRUCT_CLK case.
>   */
>  
> +struct clk {
> +	const struct clk_operations *ops;
> +};
> +
> +struct clk_operations {
> +       int             (*enable)(struct clk *);

Personaly I'd leave the enable/disable as one call which takes
(struct clk *, bool on). these code paths tend to be pretty much the
same read/modify/write with only the modify changing depending on the
on parameter.

> +       void            (*disable)(struct clk *);
> +       unsigned long   (*get_rate)(struct clk *);
> +       void            (*put)(struct clk *);
> +       long            (*round_rate)(struct clk *, unsigned long);
> +       int             (*set_rate)(struct clk *, unsigned long);
> +       int             (*set_parent)(struct clk *, struct clk *);
> +       struct clk*     (*get_parent)(struct clk *);
> +};
> +
> +static inline int clk_enable(struct clk *clk)
> +{
> +	if (clk->ops->enable)
> +		return clk->ops->enable(clk);
> +	return 0;
> +}
> +
> +static inline void clk_disable(struct clk *clk)
> +{
> +	if (clk->ops->disable)
> +		clk->ops->disable(clk);
> +}
> +
> +static inline unsigned long clk_get_rate(struct clk *clk)
> +{
> +	if (clk->ops->get_rate)
> +		return clk->ops->get_rate(clk);
> +	return 0;
> +}
> +
> +static inline void clk_put(struct clk *clk)
> +{
> +	if (clk->ops->put)
> +		clk->ops->put(clk);
> +}
> +
> +static inline long clk_round_rate(struct clk *clk, unsigned long rate)
> +{
> +	if (clk->ops->round_rate)
> +		return clk->ops->round_rate(clk, rate);
> +	return -ENOSYS;
> +}
> +
> +static inline int clk_set_rate(struct clk *clk, unsigned long rate)
> +{
> +	if (clk->ops->set_rate)
> +		return clk->ops->set_rate(clk, rate);
> +	return -ENOSYS;
> +}
> +
> +static inline int clk_set_parent(struct clk *clk, struct clk *parent)
> +{
> +	if (clk->ops->set_parent)
> +		return clk->ops->set_parent(clk, parent);
> +	return -ENOSYS;
> +}
> +
> +static inline struct clk *clk_get_parent(struct clk *clk)
> +{
> +	if (clk->ops->get_parent)
> +		return clk->ops->get_parent(clk);
> +	return ERR_PTR(-ENOSYS);
> +}

In the Samsung impelemtnations, the clk keeps a parent pointer and
we just return that as the esult of the clk_get_parent nless the clock
wants to override it.

> +
> +#else /* !CONFIG_USE_COMMON_STRUCT_CLK */
>  
>  /*
> - * struct clk - an machine class defined object / cookie.
> + * Global clock object, actual structure is declared per-machine
>   */
>  struct clk;
>  
>  /**
> - * clk_get - lookup and obtain a reference to a clock producer.
> - * @dev: device for clock "consumer"
> - * @id: clock comsumer ID
> - *
> - * Returns a struct clk corresponding to the clock producer, or
> - * valid IS_ERR() condition containing errno.  The implementation
> - * uses @dev and @id to determine the clock consumer, and thereby
> - * the clock producer.  (IOW, @id may be identical strings, but
> - * clk_get may return different clock producers depending on @dev.)
> - *
> - * Drivers must assume that the clock source is not enabled.
> - *
> - * clk_get should not be called from within interrupt context.
> - */
> -struct clk *clk_get(struct device *dev, const char *id);
> -
> -/**
>   * clk_enable - inform the system when the clock source should be running.
>   * @clk: clock source
>   *
> @@ -83,12 +148,6 @@ unsigned long clk_get_rate(struct clk *clk);
>   */
>  void clk_put(struct clk *clk);
>  
> -
> -/*
> - * The remaining APIs are optional for machine class support.
> - */
> -
> -
>  /**
>   * clk_round_rate - adjust a rate to the exact rate a clock can provide
>   * @clk: clock source
> @@ -125,6 +184,27 @@ int clk_set_parent(struct clk *clk, struct clk *parent);
>   */
>  struct clk *clk_get_parent(struct clk *clk);
>  
> +#endif /* !CONFIG_USE_COMMON_STRUCT_CLK */
> +
> +struct device;
> +
> +/**
> + * clk_get - lookup and obtain a reference to a clock producer.
> + * @dev: device for clock "consumer"
> + * @id: clock comsumer ID
> + *
> + * Returns a struct clk corresponding to the clock producer, or
> + * valid IS_ERR() condition containing errno.  The implementation
> + * uses @dev and @id to determine the clock consumer, and thereby
> + * the clock producer.  (IOW, @id may be identical strings, but
> + * clk_get may return different clock producers depending on @dev.)
> + *
> + * Drivers must assume that the clock source is not enabled.
> + *
> + * clk_get should not be called from within interrupt context.
> + */
> +struct clk *clk_get(struct device *dev, const char *id);
> +
>  /**
>   * clk_get_sys - get a clock based upon the device name
>   * @dev_id: device name
> 
> _______________________________________________
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> [email-masked]
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

-- 
-- 
Ben

Q:      What's a light-year?
A:      One-third less calories than a regular year.