From: Alexandre Belloni <alexandre.belloni@bootlin.com>
Date: Fri, 26 Apr 2019 23:47:12 +0200
Subject: [PATCH 03/10] clocksource/drivers/tcb_clksrc: Use tcb as sched_clock
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.0/older/patches-5.0.10-rt7.tar.xz

Now that the driver is registered early enough, use the TCB as the
sched_clock which is much more accurate than the jiffies implementation.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/clocksource/tcb_clksrc.c |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

--- a/drivers/clocksource/tcb_clksrc.c
+++ b/drivers/clocksource/tcb_clksrc.c
@@ -11,6 +11,7 @@
 #include <linux/io.h>
 #include <linux/of_address.h>
 #include <linux/of_irq.h>
+#include <linux/sched_clock.h>
 #include <linux/syscore_ops.h>
 #include <soc/at91/atmel_tcb.h>
 
@@ -114,6 +115,16 @@ static struct clocksource clksrc = {
 	.resume		= tc_clksrc_resume,
 };
 
+static u64 notrace tc_sched_clock_read(void)
+{
+	return tc_get_cycles(&clksrc);
+}
+
+static u64 notrace tc_sched_clock_read32(void)
+{
+	return tc_get_cycles32(&clksrc);
+}
+
 #ifdef CONFIG_GENERIC_CLOCKEVENTS
 
 struct tc_clkevt_device {
@@ -335,6 +346,7 @@ static int __init tcb_clksrc_init(struct
 	struct atmel_tc tc;
 	struct clk *t0_clk;
 	const struct of_device_id *match;
+	u64 (*tc_sched_clock)(void);
 	u32 rate, divided_rate = 0;
 	int best_divisor_idx = -1;
 	int clk32k_divisor_idx = -1;
@@ -419,6 +431,7 @@ static int __init tcb_clksrc_init(struct
 		clksrc.read = tc_get_cycles32;
 		/* setup ony channel 0 */
 		tcb_setup_single_chan(&tc, best_divisor_idx);
+		tc_sched_clock = tc_sched_clock_read32;
 	} else {
 		/* we have three clocks no matter what the
 		 * underlying platform supports.
@@ -430,6 +443,7 @@ static int __init tcb_clksrc_init(struct
 		}
 		/* setup both channel 0 & 1 */
 		tcb_setup_dual_chan(&tc, best_divisor_idx);
+		tc_sched_clock = tc_sched_clock_read;
 	}
 
 	/* and away we go! */
@@ -442,6 +456,8 @@ static int __init tcb_clksrc_init(struct
 	if (ret)
 		goto err_unregister_clksrc;
 
+	sched_clock_register(tc_sched_clock, 32, divided_rate);
+
 	return 0;
 
 err_unregister_clksrc: