clocksource/drivers/exynos_mct: Support frc-shared property

When the FRC is shared with another main processor, the other processor
is assumed to have started it and this processor should not write to the
global registers.
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Link: https://lore.kernel.org/r/20220609112738.359385-3-vincent.whitchurch@axis.comSigned-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/exynos_mct.c

@@ -233,9 +233,16 @@ static cycles_t exynos4_read_current_timer(void)
 }
 #endif
 
-static int __init exynos4_clocksource_init(void)
+static int __init exynos4_clocksource_init(bool frc_shared)
 {
-	exynos4_mct_frc_start();
+	/*
+	 * When the frc is shared, the main processer should have already
+	 * turned it on and we shouldn't be writing to TCON.
+	 */
+	if (frc_shared)
+		mct_frc.resume = NULL;
+	else
+		exynos4_mct_frc_start();
 
 #if defined(CONFIG_ARM)
 	exynos4_delay_timer.read_current_timer = &exynos4_read_current_timer;
@@ -605,6 +612,7 @@ static int __init exynos4_timer_interrupts(struct device_node *np,
 
 static int __init mct_init_dt(struct device_node *np, unsigned int int_type)
 {
+	bool frc_shared = of_property_read_bool(np, "samsung,frc-shared");
 	int ret;
 
 	ret = exynos4_timer_resources(np);
@@ -615,10 +623,17 @@ static int __init mct_init_dt(struct device_node *np, unsigned int int_type)
 	if (ret)
 		return ret;
 
-	ret = exynos4_clocksource_init();
+	ret = exynos4_clocksource_init(frc_shared);
 	if (ret)
 		return ret;
 
+	/*
+	 * When the FRC is shared with a main processor, this secondary
+	 * processor cannot use the global comparator.
+	 */
+	if (frc_shared)
+		return ret;
+
 	return exynos4_clockevent_init();
 }