linux-kernel - [PATCH 22/25] clocksource/drivers/tegra: Cycles can't be 0

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Message-Id: <20190626144651.16742-22-daniel.lezcano@linaro.org>
Date:   Wed, 26 Jun 2019 16:46:48 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, Dmitry Osipenko <digetx@...il.com>,
        Jon Hunter <jonathanh@...dia.com>,
        Thierry Reding <treding@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-tegra@...r.kernel.org (open list:TEGRA ARCHITECTURE SUPPORT)
Subject: [PATCH 22/25] clocksource/drivers/tegra: Cycles can't be 0

From: Dmitry Osipenko <digetx@...il.com>

Tegra's timer uses n+1 scheme for the counter, i.e. timer will fire after
one tick if 0 is loaded. The minimum and maximum numbers of oneshot ticks
are defined by clockevents_config_and_register(min, max) invocation and
the min value is set to 1 tick. Hence "cycles" value can't ever be 0,
unless it's a bug in clocksource core.

Signed-off-by: Dmitry Osipenko <digetx@...il.com>
Acked-by: Jon Hunter <jonathanh@...dia.com>
Acked-by: Thierry Reding <treding@...dia.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
---
 drivers/clocksource/timer-tegra.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/clocksource/timer-tegra.c b/drivers/clocksource/timer-tegra.c
index 8e70f38f1898..a907e71065bd 100644
--- a/drivers/clocksource/timer-tegra.c
+++ b/drivers/clocksource/timer-tegra.c
@@ -56,9 +56,16 @@ static int tegra_timer_set_next_event(unsigned long cycles,
 {
 	void __iomem *reg_base = timer_of_base(to_timer_of(evt));
 
-	writel_relaxed(TIMER_PTV_EN |
-		       ((cycles > 1) ? (cycles - 1) : 0), /* n+1 scheme */
-		       reg_base + TIMER_PTV);
+	/*
+	 * Tegra's timer uses n+1 scheme for the counter, i.e. timer will
+	 * fire after one tick if 0 is loaded.
+	 *
+	 * The minimum and maximum numbers of oneshot ticks are defined
+	 * by clockevents_config_and_register(1, 0x1fffffff + 1) invocation
+	 * below in the code. Hence the cycles (ticks) can't be outside of
+	 * a range supportable by hardware.
+	 */
+	writel_relaxed(TIMER_PTV_EN | (cycles - 1), reg_base + TIMER_PTV);
 
 	return 0;
 }
-- 
2.17.1