[RFC,PATCH 1/2] Add a common struct clk

[Jeremy Kerr]

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 {
	struct clk_operations *ops;
	atomic_t enable_count;
};

And a set of clock operations (defined per type of clock):

struct clk_operations {
       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_operations clk_foo_ops = {
	.get_rate = clk_foo_get_rate,
};

The common clock definitions are based on a development patch from Ben
Herrenschmidt <benh at kernel.crashing.org>.

Signed-off-by: Jeremy Kerr <jeremy.kerr at canonical.com>

---
 arch/Kconfig        |    3 
 include/linux/clk.h |  148 +++++++++++++++++++++++++++++++++++---------
 2 files changed, 124 insertions(+), 27 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index acda512..2458b5e 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -151,4 +151,7 @@ config HAVE_MIXED_BREAKPOINTS_REGS
 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..f70137a 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 at 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
@@ -11,36 +12,114 @@
 #ifndef __LINUX_CLK_H
 #define __LINUX_CLK_H
 
-struct device;
+#include <linux/err.h>
+#include <asm/atomic.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;
+	atomic_t enable_count;
+};
+
+#define DEFINE_CLK(o) \
+	{ .ops = &o, .enable_count = ATOMIC_INIT(0) }
+
+struct clk_operations {
+       int             (*enable)(struct clk *);
+       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 0;
+
+	if (atomic_inc_return(&clk->enable_count) != 1)
+		return 0;
+
+	return clk->ops->enable(clk);
+}
+
+static inline void clk_disable(struct clk *clk)
+{
+	if (!clk->ops->disable)
+		return;
+
+	if (atomic_dec_return(&clk->enable_count) != 0)
+		return;
+
+	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);
+}
+
+#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 +162,6 @@ 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 +198,27 @@ 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