[PATCH v2] clocksource: exynos-mct: Register the timer for stable udelay

[amit.daniel@samsung.com (Amit Daniel Kachhap)]

This patch register the exynos mct clocksource as the current timer
as it has constant clock rate. This will generate correct udelay for the
exynos platform and avoid using unnecessary calibrated jiffies. This change
has been tested on exynos5420 based board and udelay is very close to
expected.

Signed-off-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
---
Changes in V2:
* Added #defines for ARM and ARM64 as pointed by Doug Anderson.

Patches from David Riley confirmed that udelay is broken in exynos5420.
Link to those patches are,
1) https://patchwork.kernel.org/patch/4344911/
2) https://patchwork.kernel.org/patch/4344881/

 drivers/clocksource/exynos_mct.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
index f71d55f..02927e2 100644
--- a/drivers/clocksource/exynos_mct.c
+++ b/drivers/clocksource/exynos_mct.c
@@ -195,10 +195,25 @@ static u64 notrace exynos4_read_sched_clock(void)
 	return exynos4_frc_read(&mct_frc);
 }
 
+static struct delay_timer exynos4_delay_timer;
+
+static unsigned long exynos4_read_current_timer(void)
+{
+#ifdef ARM
+	return __raw_readl(reg_base + EXYNOS4_MCT_G_CNT_L);
+#else /* ARM64, etc */
+	return exynos4_frc_read(&mct_frc);
+#endif
+}
+
 static void __init exynos4_clocksource_init(void)
 {
 	exynos4_mct_frc_start();
 
+	exynos4_delay_timer.read_current_timer = &exynos4_read_current_timer;
+	exynos4_delay_timer.freq = clk_rate;
+	register_current_timer_delay(&exynos4_delay_timer);
+
 	if (clocksource_register_hz(&mct_frc, clk_rate))
 		panic("%s: can't register clocksource\n", mct_frc.name);
 
-- 
1.9.1