clocksource: add common of_clksrc_init() function

It is desirable to move all clocksource drivers to drivers/clocksource,
yet each requires its own initialization function. We'd rather not
pollute <linux/> with a header for each function. Instead, create a
single of_clksrc_init() function which will determine which clocksource
driver to initialize based on device tree.

Based on a similar patch for drivers/irqchip by Thomas Petazzoni.
Signed-off-by: Stephen Warren <swarren@nvidia.com>

drivers/clocksource/Kconfig

+config CLKSRC_OF
+	bool
+
 config CLKSRC_I8253
 	bool
 

drivers/clocksource/Makefile

+obj-$(CONFIG_CLKSRC_OF)	+= clksrc-of.o
 obj-$(CONFIG_ATMEL_TCB_CLKSRC)	+= tcb_clksrc.o
 obj-$(CONFIG_X86_CYCLONE_TIMER)	+= cyclone.o
 obj-$(CONFIG_X86_PM_TIMER)	+= acpi_pm.o

drivers/clocksource/clksrc-of.c

+/*
+ * Copyright (c) 2012, NVIDIA CORPORATION.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/init.h>
+#include <linux/of.h>
+
+extern struct of_device_id __clksrc_of_table[];
+
+static const struct of_device_id __clksrc_of_table_sentinel
+	__used __section(__clksrc_of_table_end);
+
+void __init clocksource_of_init(void)
+{
+	struct device_node *np;
+	const struct of_device_id *match;
+	void (*init_func)(void);
+
+	for_each_matching_node_and_match(np, __clksrc_of_table, &match) {
+		init_func = match->data;
+		init_func();
+	}
+}

include/asm-generic/vmlinux.lds.h

@@ -149,6 +149,14 @@
 #define TRACE_SYSCALLS()
 #endif
 
+#ifdef CONFIG_CLKSRC_OF
+#define CLKSRC_OF_TABLES() . = ALIGN(8);				\
+			   VMLINUX_SYMBOL(__clksrc_of_table) = .;	\
+			   *(__clksrc_of_table)				\
+			   *(__clksrc_of_table_end)
+#else
+#define CLKSRC_OF_TABLES()
+#endif
 
 #define KERNEL_DTB()							\
 	STRUCT_ALIGN();							\
@@ -493,6 +501,7 @@
 	DEV_DISCARD(init.rodata)					\
 	CPU_DISCARD(init.rodata)					\
 	MEM_DISCARD(init.rodata)					\
+	CLKSRC_OF_TABLES()						\
 	KERNEL_DTB()
 
 #define INIT_TEXT							\

include/linux/clocksource.h

@@ -332,4 +332,13 @@ extern int clocksource_mmio_init(void __iomem *, const char *,
 
 extern int clocksource_i8253_init(void);
 
+#ifdef CONFIG_CLKSRC_OF
+extern void clocksource_of_init(void);
+
+#define CLOCKSOURCE_OF_DECLARE(name, compat, fn)			\
+	static const struct of_device_id __clksrc_of_table_##name	\
+		__used __section(__clksrc_of_table)			\
+		 = { .compatible = compat, .data = fn };
+#endif
+
 #endif /* _LINUX_CLOCKSOURCE_H */