clocksource / ACPI: Add probing infrastructure for ACPI-based clocksources

DT enjoys a rather nice probing infrastructure for clocksources,
while ACPI is so far stuck into a very distant past.

This patch introduces a declarative API, allowing clocksources
to be self-contained and be called when parsing the GTDT table.
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/clocksource/clksrc-of.c

@@ -14,6 +14,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include <linux/acpi.h>
 #include <linux/init.h>
 #include <linux/of.h>
 #include <linux/clocksource.h>
@@ -38,6 +39,9 @@ void __init clocksource_of_init(void)
 		init_func(np);
 		clocksources++;
 	}
+
+	clocksources += acpi_probe_device_table(clksrc);
+
 	if (!clocksources)
 		pr_crit("%s: no matching clocksources found\n", __func__);
 }

include/asm-generic/vmlinux.lds.h

@@ -525,6 +525,7 @@
 	KERNEL_DTB()							\
 	IRQCHIP_OF_MATCH_TABLE()					\
 	ACPI_PROBE_TABLE(irqchip)					\
+	ACPI_PROBE_TABLE(clksrc)					\
 	EARLYCON_TABLE()						\
 	EARLYCON_OF_TABLES()
 

include/linux/clocksource.h

@@ -258,4 +258,7 @@ void acpi_generic_timer_init(void);
 static inline void acpi_generic_timer_init(void) { }
 #endif
 
+#define CLOCKSOURCE_ACPI_DECLARE(name, table_id, fn)		\
+	ACPI_DECLARE_PROBE_ENTRY(clksrc, name, table_id, 0, NULL, 0, fn)
+
 #endif /* _LINUX_CLOCKSOURCE_H */