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SubjectRe: [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@kernel.crashing.org>.
>
> Signed-off-by: Jeremy Kerr <jeremy.kerr@canonical.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@canonical.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@canonical.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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--
Bluewater Systems Ltd - ARM Technology Solution Centre

Ryan Mallon 5 Amuri Park, 404 Barbadoes St
ryan@bluewatersys.com PO Box 13 889, Christchurch 8013
http://www.bluewatersys.com New Zealand
Phone: +64 3 3779127 Freecall: Australia 1800 148 751
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