linux-kernel - [PATCH] clocksource: tegra186: avoid 64-bit division

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Message-Id: <20250620111939.3395525-1-arnd@kernel.org>
Date: Fri, 20 Jun 2025 13:19:35 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Thierry Reding <thierry.reding@...il.com>,
	Jonathan Hunter <jonathanh@...dia.com>,
	Pohsun Su <pohsuns@...dia.com>,
	Robert Lin <robelin@...dia.com>
Cc: Arnd Bergmann <arnd@...db.de>,
	linux-kernel@...r.kernel.org,
	linux-tegra@...r.kernel.org
Subject: [PATCH] clocksource: tegra186: avoid 64-bit division

From: Arnd Bergmann <arnd@...db.de>

The newly added function causes a build failure on 32-bit targets with
older compiler version such as gcc-10:

arm-linux-gnueabi-ld: drivers/clocksource/timer-tegra186.o: in function `tegra186_wdt_get_timeleft':
timer-tegra186.c:(.text+0x3c2): undefined reference to `__aeabi_uldivmod'

The calculation can trivially be changed to avoid the division entirely,
as USEC_PER_SEC is a multiple of 5. Change both such calculation for
consistency, even though gcc apparently managed to optimize the other one
properly already.

Fixes: 28c842c8b0f5 ("clocksource/drivers/timer-tegra186: Add WDIOC_GETTIMELEFT support")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/clocksource/timer-tegra186.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/clocksource/timer-tegra186.c b/drivers/clocksource/timer-tegra186.c
index e5394f98a02e..bd3d443e41cd 100644
--- a/drivers/clocksource/timer-tegra186.c
+++ b/drivers/clocksource/timer-tegra186.c
@@ -159,7 +159,7 @@ static void tegra186_wdt_enable(struct tegra186_wdt *wdt)
 	tmr_writel(wdt->tmr, TMRCSSR_SRC_USEC, TMRCSSR);
 
 	/* configure timer (system reset happens on the fifth expiration) */
-	value = TMRCR_PTV(wdt->base.timeout * USEC_PER_SEC / 5) |
+	value = TMRCR_PTV(wdt->base.timeout * (USEC_PER_SEC / 5)) |
 		TMRCR_PERIODIC | TMRCR_ENABLE;
 	tmr_writel(wdt->tmr, value, TMRCR);
 
@@ -267,7 +267,7 @@ static unsigned int tegra186_wdt_get_timeleft(struct watchdog_device *wdd)
 	 * counter value to the time of the counter expirations that
 	 * remain.
 	 */
-	timeleft += (((u64)wdt->base.timeout * USEC_PER_SEC) / 5) * (4 - expiration);
+	timeleft += (u64)wdt->base.timeout * (USEC_PER_SEC / 5) * (4 - expiration);
 
 	/*
 	 * Convert the current counter value to seconds,
-- 
2.39.5