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clocksource/drivers/timer-tegra186: Simplify calculating timeleft 

It is not necessary to use 64-bit operations to calculate the
remaining watchdog timeout. Simplify to use 32-bit operations,
and add comments explaining why there will be no overflow.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Cc: Pohsun Su <pohsuns@nvidia.com>
Cc: Robert Lin <robelin@nvidia.com>
Link: https://lore.kernel.org/r/20250614175556.922159-2-linux@roeck-us.net
This commit is contained in:
Guenter Roeck 2025-06-14 10:55:56 -07:00 committed by Daniel Lezcano
parent 916aa36042
commit 7f3abae5b4
1 changed files with 15 additions and 10 deletions
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25
drivers/clocksource/timer-tegra186.c
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@ -231,7 +231,7 @@ static unsigned int tegra186_wdt_get_timeleft(struct watchdog_device *wdd)
{
struct tegra186_wdt *wdt = to_tegra186_wdt(wdd);
u32 expiration, val;
u64 timeleft;
u32 timeleft;
if (!watchdog_active(&wdt->base)) {
/* return zero if the watchdog timer is not activated. */
@ -266,21 +266,26 @@ static unsigned int tegra186_wdt_get_timeleft(struct watchdog_device *wdd)
* Calculate the time remaining by adding the time for the
* counter value to the time of the counter expirations that
* remain.
* Note: Since wdt->base.timeout is bound to 255, the maximum
* value added to timeleft is
* 255 * (1,000,000 / 5) * 4
* = 255 * 200,000 * 4
* = 204,000,000
* TMRSR_PCV is a 29-bit field.
* Its maximum value is 0x1fffffff = 536,870,911.
* 204,000,000 + 536,870,911 = 740,870,911 = 0x2C28CAFF.
* timeleft can therefore not overflow, and 64-bit calculations
* are not necessary.
*/
timeleft += ((u64)wdt->base.timeout * (USEC_PER_SEC / 5)) * (4 - expiration);
timeleft += (wdt->base.timeout * (USEC_PER_SEC / 5)) * (4 - expiration);
/*
* Convert the current counter value to seconds,
* rounding up to the nearest second. Cast u64 to
* u32 under the assumption that no overflow happens
* when coverting to seconds.
* rounding to the nearest second.
*/
timeleft = DIV_ROUND_CLOSEST_ULL(timeleft, USEC_PER_SEC);
timeleft = DIV_ROUND_CLOSEST(timeleft, USEC_PER_SEC);
if (WARN_ON_ONCE(timeleft > U32_MAX))
return U32_MAX;
return lower_32_bits(timeleft);
return timeleft;
}
static const struct watchdog_ops tegra186_wdt_ops = {