Re: [PATCH 1/2] Add a common struct clk

From: Uwe Kleine-König
Date: Wed Dec 08 2010 - 05:21:57 EST

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Hi Jeremy,

On Wed, Dec 08, 2010 at 10:05:32AM +0800, 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.
>
> 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;
> int flags;
> union {
> struct mutex mutex;
> spinlock_t spinlock;
> } 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@xxxxxxxxxxxxxxxxxxx>.
>
> Signed-off-by: Jeremy Kerr <jeremy.kerr@xxxxxxxxxxxxx>
> Acked-by: Paulius Zaleckas <paulius.zaleckas@xxxxxxxxx>
>
> ---
> arch/Kconfig | 3
> include/linux/clk.h | 158 +++++++++++++++++++++++++++++++++++++++++---
> kernel/Makefile | 1
> kernel/clk.c | 100 +++++++++++++++++++++++++++
> 4 files changed, 253 insertions(+), 9 deletions(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 8bf0fa6..212bd3c 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -165,6 +165,9 @@ config HAVE_MIXED_BREAKPOINTS_REGS
> config HAVE_USER_RETURN_NOTIFIER
> bool
>
> +config USE_COMMON_STRUCT_CLK
> + bool
> +
> config HAVE_PERF_EVENTS_NMI
> bool
> help
> diff --git a/include/linux/clk.h b/include/linux/clk.h
> index 1d37f42..e09e40e 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 Jeremy Kerr <jeremy.kerr@xxxxxxxxxxxxx>
> *
> * 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 +12,163 @@
> #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
> +
> +#define CLK_ATOMIC 0x1
> +
> +/* If we're using the common struct clk, we define the base clk object here */
> +
> +/**
> + * struct clk - hardware independent clock structure
> + * @clk_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.
> + */
> +struct clk {
> + const struct clk_ops *ops;
> + unsigned int enable_count;
> + int flags;
> + union {
> + struct mutex mutex;
> + spinlock_t spinlock;
> + } lock;
> +};
> +
> +/* static initialiser for non-atomic clocks */
> +#define INIT_CLK(name, o) { \
> + .ops = &o, \
> + .enable_count = 0, \
> + .flags = 0, \
> + .lock.mutex = __MUTEX_INITIALIZER(name.lock.mutex), \
> +}
> +
> +/* static initialiser for atomic clocks */
> +#define INIT_CLK_ATOMIC(name, o) { \
> + .ops = &o, \
> + .enable_count = 0, \
> + .flags = CLK_ATOMIC, \
> + .lock.spinlock = __SPIN_LOCK_UNLOCKED(name.lock.spinlock), \
> +}
> +
> +/**
> + * 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.
> + *
> + * @enable: Enable the clock. This must not return until the clock is
> + * generating a valid clock signal, usable by consumer devices.
> + * Called with clk->lock held.
> + *
> + * @disable: Disable the clock. Called with clk->lock held.
> + *
> + * @get / @put: Called by the core clock code to notify the driver about
I wonder if this is valid kerneldoc. The tab before / looks (IMHO)
ugly. Maybe specify "driver" a bit more to distinguish from "drivers"
above. "clk_ops driver"?

> + * refounts as clk is passed to drivers. Optional.
> + *
> + * For other callbacks, see the corresponding clk_* functions. Parameters and
> + * return values are passed directly from/to these API functions directly, or
duplicated "directly"
> + * -ENOSYS is returned if the callback is NULL, see kernel/clk.c for
> + * implementation details. All are optional.
> */
> +struct clk_ops {
> + 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 *);
> +};
>
> +static inline void __clk_lock(struct clk *clk)
> +{
> + if (clk->flags & CLK_ATOMIC)
> + spin_lock(&clk->lock.spinlock);
> + else
> + mutex_lock(&clk->lock.mutex);
> +}
> +
> +static inline void __clk_unlock(struct clk *clk)
> +{
> + if (clk->flags & CLK_ATOMIC)
> + spin_unlock(&clk->lock.spinlock);
> + else
> + mutex_unlock(&clk->lock.mutex);
> +}
> +
> +/**
> + * __clk_get - update clock-specific refcounter
> + *
> + * @clk: The clock to refcount
"The clock to update the refcount for"?

> + *
> + * 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);
> +
> +/**
> + * clk_common_init - initialise a clock for driver usage
> + *
> + * 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 = 0;
> + if (clk->flags & CLK_ATOMIC)
> + spin_lock_init(&clk->lock.spinlock);
> + else
> + mutex_init(&clk->lock.mutex);
> +}
> +
> +#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) { }
> +
> +#endif /* !CONFIG_USE_COMMON_STRUCT_CLK */
> +
> /**
> * clk_get - lookup and obtain a reference to a clock producer.
> * @dev: device for clock "consumer"
> @@ -83,12 +229,6 @@ 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
> diff --git a/kernel/Makefile b/kernel/Makefile
> index 0b5ff08..01383a0 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -106,6 +106,7 @@ obj-$(CONFIG_PERF_EVENTS) += perf_event.o
> obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
> obj-$(CONFIG_USER_RETURN_NOTIFIER) += user-return-notifier.o
> obj-$(CONFIG_PADATA) += padata.o
> +obj-$(CONFIG_USE_COMMON_STRUCT_CLK) += clk.o
>
> ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y)
> # According to Alan Modra <alan@xxxxxxxxxxxxxxxx>, the -fno-omit-frame-pointer is
> diff --git a/kernel/clk.c b/kernel/clk.c
> new file mode 100644
> index 0000000..1545e69
> --- /dev/null
> +++ b/kernel/clk.c
> @@ -0,0 +1,100 @@
> +/*
> + * Copyright (C) 2010 Canonical Ltd <jeremy.kerr@xxxxxxxxxxxxx>
> + *
> + * 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_enable(struct clk *clk)
> +{
> + int ret = 0;
> +
> + if (!clk->ops->enable)
> + return 0;
> +
> + __clk_lock(clk);
> + if (!clk->enable_count)
> + ret = clk->ops->enable(clk);
I wonder if it's worth to handle parents here, e.g.

if (!clk->enable_count) {
struct clk *parent = clk_get_parent(clk);
if (parent) {
ret = clk_enable(parent);
if (ret)
return ret;
}

ret = clk->ops->enable(clk);
if (likely(!ret))
clk->enable_count++;
else if (parent)
clk_disable(parent);
}

as they are quite common.

And I wonder further if it makes the code a bit more efficient to use:

if (!clk->enable_count++) {
... enable clock (and maybe parent)
if (unlikely(ret))
clk->enable_count--
...

> +
> + if (!ret)
> + clk->enable_count++;
> + __clk_unlock(clk);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(clk_enable);
> +
> +void clk_disable(struct clk *clk)
> +{
> + if (!clk->ops->disable)
> + return;

WARN_ON(!clk->enable_count) ?
> +
> + __clk_lock(clk);
> +
> + if (!--clk->enable_count)
> + clk->ops->disable(clk);
> +
> + __clk_unlock(clk);
> +}
> +EXPORT_SYMBOL_GPL(clk_disable);
> +
> +unsigned long clk_get_rate(struct clk *clk)
> +{
> + if (clk->ops->get_rate)
> + return clk->ops->get_rate(clk);
> + 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);
> +
> +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);
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>

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Industrial Linux Solutions | http://www.pengutronix.de/ |
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