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Subject[PATCH] tcb_clksrc: Use 32 bit tcb as sched_clock
Date
On newer boards the TC can be read as single 32 bit value without locking.
Thus the clock can be used as reference for sched_clock which is much more
accurate than the jiffies implementation.

Tested on a Atmel SAMA5D2 board.

Signed-off-by: David Engraf <david.engraf@sysgo.com>
---
drivers/clocksource/tcb_clksrc.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/clocksource/tcb_clksrc.c b/drivers/clocksource/tcb_clksrc.c
index d4ca996..745844e 100644
--- a/drivers/clocksource/tcb_clksrc.c
+++ b/drivers/clocksource/tcb_clksrc.c
@@ -10,6 +10,7 @@
#include <linux/io.h>
#include <linux/platform_device.h>
#include <linux/atmel_tc.h>
+#include <linux/sched_clock.h>


/*
@@ -56,11 +57,16 @@ static u64 tc_get_cycles(struct clocksource *cs)
return (upper << 16) | lower;
}

-static u64 tc_get_cycles32(struct clocksource *cs)
+static u32 tc_get_cv32(void)
{
return __raw_readl(tcaddr + ATMEL_TC_REG(0, CV));
}

+static u64 tc_get_cycles32(struct clocksource *cs)
+{
+ return tc_get_cv32();
+}
+
static struct clocksource clksrc = {
.name = "tcb_clksrc",
.rating = 200,
@@ -69,6 +75,11 @@ static struct clocksource clksrc = {
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
};

+static u64 notrace tc_read_sched_clock(void)
+{
+ return tc_get_cv32();
+}
+
#ifdef CONFIG_GENERIC_CLOCKEVENTS

struct tc_clkevt_device {
@@ -339,6 +350,9 @@ static int __init tcb_clksrc_init(void)
clksrc.read = tc_get_cycles32;
/* setup ony channel 0 */
tcb_setup_single_chan(tc, best_divisor_idx);
+
+ /* register sched_clock on chips with single 32 bit counter */
+ sched_clock_register(tc_read_sched_clock, 32, divided_rate);
} else {
/* tclib will give us three clocks no matter what the
* underlying platform supports.
--
2.9.3
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