ARM: 7451/1: arch timer: implement read_current_timer and get_cycles

This patch implements read_current_timer using the architected timers
when they are selected via CONFIG_ARM_ARCH_TIMER. If they are detected
not to be usable at runtime, we return -ENXIO to the caller.

Furthermore, if read_current_timer is exported then we can implement
get_cycles in terms of it for use as both an entropy source and for
implementing __udelay and friends.

Tested-by: Shinya Kuribayashi <shinya.kuribayashi.px@renesas.com>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

3 files changed, 17 insertions, 4 deletions

diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
index ed2e95d46e29..62e75475e57e 100644
--- a/arch/arm/include/asm/arch_timer.h
+++ b/arch/arm/include/asm/arch_timer.h
@@ -1,7 +1,10 @@
 #ifndef __ASMARM_ARCH_TIMER_H
 #define __ASMARM_ARCH_TIMER_H
 
+#include <asm/errno.h>
+
 #ifdef CONFIG_ARM_ARCH_TIMER
+#define ARCH_HAS_READ_CURRENT_TIMER
 int arch_timer_of_register(void);
 int arch_timer_sched_clock_init(void);
 #else
diff --git a/arch/arm/include/asm/timex.h b/arch/arm/include/asm/timex.h
index 3be8de3adaba..ce119442277c 100644
--- a/arch/arm/include/asm/timex.h
+++ b/arch/arm/include/asm/timex.h
@@ -12,13 +12,15 @@
 #ifndef _ASMARM_TIMEX_H
 #define _ASMARM_TIMEX_H
 
+#include <asm/arch_timer.h>
 #include <mach/timex.h>
 
 typedef unsigned long cycles_t;
 
-static inline cycles_t get_cycles (void)
-{
-        return 0;
-}
+#ifdef ARCH_HAS_READ_CURRENT_TIMER
+#define get_cycles()    ({ cycles_t c; read_current_timer(&c) ? 0 : c; })
+#else
+#define get_cycles()    (0)
+#endif
 
 #endif
diff --git a/arch/arm/kernel/arch_timer.c b/arch/arm/kernel/arch_timer.c
index dd58035621f7..dbbeec4f06e2 100644
--- a/arch/arm/kernel/arch_timer.c
+++ b/arch/arm/kernel/arch_timer.c
@@ -223,6 +223,14 @@ static cycle_t arch_counter_read(struct clocksource *cs)
         return arch_counter_get_cntpct();
 }
 
+int read_current_timer(unsigned long *timer_val)
+{
+        if (!arch_timer_rate)
+                return -ENXIO;
+        *timer_val = arch_counter_get_cntpct();
+        return 0;
+}
+
 static struct clocksource clocksource_counter = {
         .name   = "arch_sys_counter",
         .rating = 400,