Message-ID: <4D50541B.2030405@bluewatersys.com>
Date:	Tue, 08 Feb 2011 09:20:43 +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>,
	Dima Zavin <dmitriyz@...gle.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-sh@...r.kernel.org,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Paul Mundt <lethal@...ux-sh.org>,
	Saravana Kannan <skannan@...eaurora.org>,
	Ben Dooks <ben-linux@...ff.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [RFC,PATCH 1/3] Add a common struct clk

On 02/07/2011 07:07 PM, 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, and impossible to compile two
> platforms with different struct clks into a single image.
> 
> 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.

Hi Jeremy,

Quick review below.

~Ryan

> Platforms can enable the generic struct clock through
> CONFIG_USE_COMMON_STRUCT_CLK. In this case, the clock infrastructure
> consists of a common struct clk:
> 
> struct clk {
> 	const struct clk_ops	*ops;
> 	unsigned int		enable_count;
> 	unsigned int		prepare_count;
> 	spinlock_t		enable_lock;
> 	struct mutex		prepare_lock;
> };
> 
> And a set of clock operations (defined per type of clock):
> 
> struct clk_ops {
> 	int             (*enable)(struct clk *);
> 	void            (*disable)(struct clk *);
> 	unsigned long   (*get_rate)(struct clk *);
> 	[...]
> };
> 
> To define a hardware-specific clock, machine code can "subclass" the
> struct clock into a new struct (adding any device-specific data), and
> provide a set of operations:
> 
> struct clk_foo {
> 	struct clk	clk;
> 	void __iomem	*some_register;
> };
> 
> struct clk_ops clk_foo_ops = {
> 	.get_rate = clk_foo_get_rate,
> };
> 
> The common clock definitions are based on a development patch from Ben
> Herrenschmidt <benh@...nel.crashing.org>.
> 
> Signed-off-by: Jeremy Kerr <jeremy.kerr@...onical.com>
> 
> ---
>  drivers/clk/Kconfig  |    3 
>  drivers/clk/Makefile |    1 
>  drivers/clk/clk.c    |  134 +++++++++++++++++++++++++++++++
>  drivers/clk/clkdev.c |    5 +
>  include/linux/clk.h  |  184 ++++++++++++++++++++++++++++++++++++++++---
>  5 files changed, 318 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
> index 4168c88..6e3ae54 100644
> --- a/drivers/clk/Kconfig
> +++ b/drivers/clk/Kconfig
> @@ -2,3 +2,6 @@
>  config CLKDEV_LOOKUP
>  	bool
>  	select HAVE_CLK
> +
> +config USE_COMMON_STRUCT_CLK
> +	bool
> diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
> index 07613fa..a1a06d3 100644
> --- a/drivers/clk/Makefile
> +++ b/drivers/clk/Makefile
> @@ -1,2 +1,3 @@
>  
>  obj-$(CONFIG_CLKDEV_LOOKUP)	+= clkdev.o
> +obj-$(CONFIG_USE_COMMON_STRUCT_CLK) += clk.o
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> new file mode 100644
> index 0000000..12e0daf
> --- /dev/null
> +++ b/drivers/clk/clk.c
> @@ -0,0 +1,134 @@
> +/*
> + * Copyright (C) 2010-2011 Canonical Ltd <jeremy.kerr@...onical.com>
> + *
> + * 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/clk.h>
> +#include <linux/module.h>
> +
> +int clk_prepare(struct clk *clk)
> +{
> +	int ret = 0;
> +
> +	if (!clk->ops->prepare)
> +		return 0;

If there is no ops->prepare function then we never increment
prepare_count, which means that driver writers can get sloppy if they
know that ops->prepare is no-op on their platform since they will not
get warned for omitting clk_prepare.

Also, why are the warnings added in a separate patch rather than being
rolled into this patch?

> +
> +	mutex_lock(&clk->prepare_lock);
> +	if (clk->prepare_count == 0)
> +		ret = clk->ops->prepare(clk);
> +
> +	if (!ret)
> +		clk->prepare_count++;
> +	mutex_unlock(&clk->prepare_lock);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(clk_prepare);
> +
> +void clk_unprepare(struct clk *clk)
> +{
> +	if (!clk->ops->unprepare)
> +		return;
> +
> +	mutex_lock(&clk->prepare_lock);
> +	if (--clk->prepare_count == 0)
> +		clk->ops->unprepare(clk);
> +
> +	mutex_unlock(&clk->prepare_lock);
> +}
> +EXPORT_SYMBOL_GPL(clk_unprepare);
> +
> +int clk_enable(struct clk *clk)
> +{
> +	int ret = 0;
> +
> +	if (!clk->ops->enable)
> +		return 0;

Again, you should still increment enable_count even if ops->enabled is a
no-op since it provides valuable warnings when clk_enable/disable calls
are not matched correctly.

> +
> +	spin_lock(&clk->enable_lock);
> +	if (!clk->enable_count)
> +		ret = clk->ops->enable(clk);
> +
> +	if (!ret)
> +		clk->enable_count++;
> +	spin_unlock(&clk->enable_lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(clk_enable);
> +
> +void clk_disable(struct clk *clk)
> +{
> +	if (!clk->ops->disable)
> +		return;
> +
> +	spin_lock(&clk->enable_lock);
> +
> +	WARN_ON(!clk->enable_count);
> +
> +	if (!--clk->enable_count)
> +		clk->ops->disable(clk);
> +
> +	spin_unlock(&clk->enable_lock);
> +}
> +EXPORT_SYMBOL_GPL(clk_disable);
> +
> +unsigned long clk_get_rate(struct clk *clk)
> +{
> +	if (clk->ops->get_rate)
> +		return clk->ops->get_rate(clk);

Possibly we should shadow the clock rate if ops->get_rate is no-op? So
clock initialisation and clk_set_rate store the rate in the shadow
field, and then do:

	if (clk->ops->get_rate)
		return clk->ops->get_rate(clk);
	return clk->shadow_rate;

Because the API is generic, driver writers should reasonably expect that
clk_get_rate will return something valid without having to know the
platform implementation details. It may also be worth having a warning
to let the user know that the returned rate may be approximate.

> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(clk_get_rate);
> +
> +int __clk_get(struct clk *clk)
> +{
> +	if (clk->ops->get)
> +		return clk->ops->get(clk);
> +	return 1;
> +}
> +EXPORT_SYMBOL_GPL(__clk_get);
> +
> +void clk_put(struct clk *clk)
> +{
> +	if (clk->ops->put)
> +		clk->ops->put(clk);
> +}
> +EXPORT_SYMBOL_GPL(clk_put);

This has probably been covered, and I have probably missed it, but why
don't the generic clk_get/put functions do ref-counting? Drivers must
have matched clk_get/put calls so it should work like enable/prepare
counting right?

> +long clk_round_rate(struct clk *clk, unsigned long rate)
> +{
> +	if (clk->ops->round_rate)
> +		return clk->ops->round_rate(clk, rate);
> +	return -ENOSYS;
> +}
> +EXPORT_SYMBOL_GPL(clk_round_rate);
> +
> +int clk_set_rate(struct clk *clk, unsigned long rate)
> +{
> +	if (clk->ops->set_rate)
> +		return clk->ops->set_rate(clk, rate);
> +	return -ENOSYS;
> +}
> +EXPORT_SYMBOL_GPL(clk_set_rate);
> +
> +int clk_set_parent(struct clk *clk, struct clk *parent)
> +{
> +	if (clk->ops->set_parent)
> +		return clk->ops->set_parent(clk, parent);
> +	return -ENOSYS;
> +}
> +EXPORT_SYMBOL_GPL(clk_set_parent);
> +
> +struct clk *clk_get_parent(struct clk *clk)
> +{
> +	if (clk->ops->get_parent)
> +		return clk->ops->get_parent(clk);
> +	return ERR_PTR(-ENOSYS);
> +}
> +EXPORT_SYMBOL_GPL(clk_get_parent);
> diff --git a/drivers/clk/clkdev.c b/drivers/clk/clkdev.c
> index 0fc0a79..17619c7 100644
> --- a/drivers/clk/clkdev.c
> +++ b/drivers/clk/clkdev.c
> @@ -84,12 +84,17 @@ struct clk *clk_get(struct device *dev, const char *con_id)
>  }
>  EXPORT_SYMBOL(clk_get);
>  
> +#ifndef CONFIG_USE_COMMON_STRUCT_CLK
> +/* For the common struct clk case, clk_put is provided by clk.c */
> +
>  void clk_put(struct clk *clk)
>  {
>  	__clk_put(clk);
>  }
>  EXPORT_SYMBOL(clk_put);
>  
> +#endif
> +
>  void clkdev_add(struct clk_lookup *cl)
>  {
>  	mutex_lock(&clocks_mutex);
> diff --git a/include/linux/clk.h b/include/linux/clk.h
> index 1d37f42..e081ca1 100644
> --- a/include/linux/clk.h
> +++ b/include/linux/clk.h
> @@ -3,6 +3,7 @@
>   *
>   *  Copyright (C) 2004 ARM Limited.
>   *  Written by Deep Blue Solutions Limited.
> + *  Copyright (c) 2010-2011 Jeremy Kerr <jeremy.kerr@...onical.com>
>   *
>   * 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
> @@ -11,18 +12,189 @@
>  #ifndef __LINUX_CLK_H
>  #define __LINUX_CLK_H
>  
> +#include <linux/err.h>
> +#include <linux/mutex.h>
> +#include <linux/spinlock.h>
> +
>  struct device;
>  
> -/*
> - * The base API.
> +#ifdef CONFIG_USE_COMMON_STRUCT_CLK
> +
> +/* If we're using the common struct clk, we define the base clk object here */
> +
> +/**
> + * struct clk - hardware independent clock structure
> + * @ops:		implementation-specific ops for this clock
> + * @enable_count:	count of clk_enable() calls active on this clock
> + * @flags:		platform-independent flags
> + * @lock:		lock for enable/disable or other HW-specific ops
> + *
> + * The base clock object, used by drivers for hardware-independent manipulation
> + * of clock lines. This will be 'subclassed' by device-specific implementations,
> + * which add device-specific data to struct clk. For example:
> + *
> + *  struct clk_foo {
> + *      struct clk;
> + *      [device specific fields]
> + *  };
> + *
> + * The clock driver code will manage the device-specific data, and pass
> + * clk_foo.clk to the common clock code. The clock driver will be called
> + * through the @ops callbacks.
> + *
> + * The @lock member provides either a spinlock or a mutex to protect (at least)
> + * @enable_count. The type of lock used will depend on @flags; if CLK_ATOMIC is
> + * set, then the core clock code will use a spinlock, otherwise a mutex. This
> + * lock will be acquired during clk_enable and clk_disable, so for atomic
> + * clocks, these ops callbacks must not sleep.
> + *
> + * The choice of atomic or non-atomic clock depends on how the clock is enabled.
> + * Typically, you'll want to use a non-atomic clock. For clocks that need to be
> + * enabled/disabled in interrupt context, use CLK_ATOMIC. Note that atomic
> + * clocks with parents will typically cascade enable/disable operations to
> + * their parent, so the parent of an atomic clock *must* be atomic too.

This comment seems out of date now that we have the prepare/enable
semantics?

>   */
> +struct clk {
> +	const struct clk_ops	*ops;
> +	unsigned int		enable_count;
> +	unsigned int		prepare_count;
> +	spinlock_t		enable_lock;
> +	struct mutex		prepare_lock;
> +};
> +
> +/* static initialiser for non-atomic clocks */
> +#define INIT_CLK(name, o) {						\
> +	.ops		= &o,						\
> +	.enable_count	= 0,						\
> +	.prepare_count	= 0,						\
> +	.enable_lock	= __SPIN_LOCK_UNLOCKED(name.enable_lock),	\
> +	.prepare_lock	= __MUTEX_INITIALIZER(name.prepare_lock),	\
> +}
>  
> +/**
> + * struct clk_ops -  Callback operations for clocks; these are to be provided
> + * by the clock implementation, and will be called by drivers through the clk_*
> + * API.
> + *
> + * @prepare:	Prepare the clock for enabling. This must not return until
> + *		the clock is fully prepared, and it's safe to call clk_enable.
> + *		This callback is intended to allow clock implementations to
> + *		do any initialisation that may block. Called with
> + *		clk->prepare_lock held.
> + *
> + * @unprepare:	Release the clock from its prepared state. This will typically
> + *		undo any work done in the @prepare callback. Called with
> + *		clk->prepare_lock held.

I think you need to make it more clear the prepare/unprepare must be
called from a sleepable context.

> + * @enable:	Enable the clock atomically. This must not return until the
> + *		clock is generating a valid clock signal, usable by consumer
> + *		devices. Called with clk->enable_lock held.
> + *
> + * @disable:	Disable the clock atomically. Called with clk->enable_lock held.
> + *
> + * @get:	Called by the core clock code when a device driver acquires a
> + *		clock via clk_get(). Optional.
> + *
> + * @put:	Called by the core clock code when a devices driver releases a
> + *		clock via clk_put(). Optional.
> + *
> + * The clk_enable/clk_disable and clk_prepare/clk_unprepare pairs allow
> + * implementations to split any work between atomic (enable) and sleepable
> + * (prepare) contexts.  If a clock requires blocking code to be turned on, this
> + * should be done in clk_prepare. Switching that will not block should be done
> + * in clk_enable.
> + *
> + * Typically, drivers will call clk_prepare when a clock may be needed later
> + * (eg. when a device is opened), and clk_enable when the clock is actually
> + * required (eg. from an interrupt).

Drivers _must_ call clk_prepare before clk_enable (not typically)?

> + *
> + * For other callbacks, see the corresponding clk_* functions. Parameters and
> + * return values are passed directly from/to these API functions, or
> + * -ENOSYS (or zero, in the case of clk_get_rate) is returned if the callback
> + * is NULL, see kernel/clk.c for implementation details. All are optional.
> + */
> +struct clk_ops {
> +	int		(*prepare)(struct clk *);
> +	void		(*unprepare)(struct clk *);
> +	int		(*enable)(struct clk *);
> +	void		(*disable)(struct clk *);
> +	int		(*get)(struct clk *);
> +	void		(*put)(struct clk *);
> +	unsigned long	(*get_rate)(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 *);
> +};
> +
> +/**
> + * __clk_get - update clock-specific refcounter
> + *
> + * @clk: The clock to refcount
> + *
> + * Before a clock is returned from clk_get, this function should be called
> + * to update any clock-specific refcounting.
> + *
> + * Returns non-zero on success, zero on failure.
> + *
> + * Drivers should not need this function; it is only needed by the
> + * arch-specific clk_get() implementations.
> + */
> +int __clk_get(struct clk *clk);

I don't understand this. Are architectures supposed to provide a
function called clk_get? Doesn't this break the whole idea of having a
common struct clk?

> +/**
> + * clk_prepare - prepare clock for atomic enabling.
> + *
> + * @clk: The clock to prepare
> + *
> + * Do any blocking initialisation on @clk, allowing the clock to be later
> + * enabled atomically (via clk_enable). This function may sleep.
> + */
> +int clk_prepare(struct clk *clk);
> +
> +/**
> + * clk_unprepare - release clock from prepared state
> + *
> + * @clk: The clock to release
> + *
> + * Do any (possbly blocking) cleanup on clk. This function may sleep.
> + */
> +void clk_unprepare(struct clk *clk);
> +
> +/**
> + * clk_common_init - initialise a clock for driver usage
> + *
> + * @clk: The clock to initialise
> + *
> + * Used for runtime intialization of clocks; you don't need to call this
> + * if your clock has been (statically) initialized with INIT_CLK.
> + */
> +static inline void clk_common_init(struct clk *clk)
> +{
> +	clk->enable_count = clk->prepare_count = 0;
> +	spin_lock_init(&clk->enable_lock);
> +	mutex_init(&clk->prepare_lock);
> +}
> +
> +#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;
>  
> +static inline void clk_common_init(struct clk *clk) { }
> +
> +/*
> + * For !CONFIG_USE_COMMON_STRUCT_CLK, we don't enforce any atomicity
> + * requirements for clk_enable/clk_disable, so the prepare and unprepare
> + * functions are no-ops
> + */
> +int clk_prepare(struct clk *clk) { return 0; }
> +void clk_unprepare(struct clk *clk) { }
> +
> +#endif /* !CONFIG_USE_COMMON_STRUCT_CLK */
> +
>  /**
>   * clk_get - lookup and obtain a reference to a clock producer.
>   * @dev: device for clock "consumer"
> @@ -83,12 +255,6 @@ 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
> --
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