Subject: Clocksource: Add sched_clock to Atmel TCB clocksource
From: Carsten Emde <[email-masked]>
Date: Sun, 31 May 2015 12:32:11 +0100

The default sched_clock provides a maximum resolution of 1 ms which
normally is not sufficient to investigate scheduling related
irregularities - more so, if a low-latency or even a real-time kernel is
used. Therefore, register the Atmel TCB clocksource that provides a
resolution of 63 ns as sched_clock.

Signed-off-by: Carsten Emde <[email-masked]>

---
 drivers/clocksource/tcb_clksrc.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

Index: linux-3.18.13-rt10-r7s4/drivers/clocksource/tcb_clksrc.c
===================================================================
--- linux-3.18.13-rt10-r7s4.orig/drivers/clocksource/tcb_clksrc.c
+++ linux-3.18.13-rt10-r7s4/drivers/clocksource/tcb_clksrc.c
@@ -10,7 +10,9 @@
 #include <linux/io.h>
 #include <linux/platform_device.h>
 #include <linux/atmel_tc.h>
+#include <linux/sched_clock.h>
 
+#define DEBUG
 
 /*
  * We're configured to use a specific TC block, one that's not hooked
@@ -69,6 +71,11 @@ static struct clocksource clksrc = {
 	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
 };
 
+static u64 sched_clock_get_cycles(void)
+{
+	return (u64) clksrc.read(NULL);
+}
+
 #ifdef CONFIG_GENERIC_CLOCKEVENTS
 
 struct tc_clkevt_device {
@@ -273,6 +280,7 @@ static int __init tcb_clksrc_init(void)
 	int clk32k_divisor_idx = -1;
 	int i;
 	int ret;
+	unsigned long flags;
 
 	tc = atmel_tc_alloc(CONFIG_ATMEL_TCB_CLKSRC_BLOCK);
 	if (!tc) {
@@ -339,6 +347,10 @@ static int __init tcb_clksrc_init(void)
 	if (ret)
 		goto err_disable_t1;
 
+	local_irq_save(flags);
+	sched_clock_register(sched_clock_get_cycles, 32, divided_rate);
+	local_irq_restore(flags);
+
 	/* channel 2:  periodic and oneshot timer support */
 	ret = setup_clkevents(tc, clk32k_divisor_idx);
 	if (ret)