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

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

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.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@arndb.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

Re: [PATCH] clocksource: tegra186: avoid 64-bit division

[Jon Hunter]

On 20/06/2025 12:19, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.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@arndb.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,


Guenter has also posted a fix for this here [0].

Jon

[0] 
https://lore.kernel.org/linux-tegra/75496de8-51fd-4e27-9f92-babaa0e22c14@nvidia.com/T/#me403a7afd04bbf24e29d3880123a4faa656eab05
-- 
nvpublic

Re: [PATCH] clocksource: tegra186: avoid 64-bit division

[Arnd Bergmann]

On Tue, Jun 24, 2025, at 12:06, Jon Hunter wrote:
> On 20/06/2025 12:19, Arnd Bergmann wrote:

>> @@ -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,
>
>
> Guenter has also posted a fix for this here [0].
>

Right, that one looks better than mine, as it avoids another
division entirely.

     Arnd

Re: [PATCH] clocksource: tegra186: avoid 64-bit division

[Daniel Lezcano]

On 6/20/25 13:19, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.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@arndb.de>
> ---

Applied, thanks

Fixed conflict with 
https://lore.kernel.org/r/20250614175556.922159-2-linux@roeck-us.net



-- 
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog