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From:   Vincent Whitchurch <vincent.whitchurch@axis.com>
To:     <krzysztof.kozlowski@linaro.org>, <tglx@linutronix.de>,
        <daniel.lezcano@linaro.org>
CC:     <kernel@axis.com>,
        Vincent Whitchurch <vincent.whitchurch@axis.com>,
        <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-samsung-soc@vger.kernel.org>, <alim.akhtar@samsung.com>,
        <devicetree@vger.kernel.org>, <robh+dt@kernel.org>
Subject: [PATCH v4 2/4] clocksource/drivers/exynos_mct: Support frc-shared property
Date:   Thu, 9 Jun 2022 13:27:36 +0200
Message-ID: <20220609112738.359385-3-vincent.whitchurch@axis.com>
In-Reply-To: <20220609112738.359385-1-vincent.whitchurch@axis.com>
References: <20220609112738.359385-1-vincent.whitchurch@axis.com>
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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>
---

Notes:
    v4:
    - Add Krzysztof's Reviewed-by.
    
    v3:
    - Split FRC sharing handling from local timer indices handling
    - Remove addition of global variable.

 drivers/clocksource/exynos_mct.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
index f29c812b70c9..12023831dedf 100644
--- a/drivers/clocksource/exynos_mct.c
+++ b/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();
 }
 
-- 
2.34.1