Re: [PATCH] watchdog: xilinx_wwdt: Use div_u64() in xilinx_wwdt_start()

[Guenter Roeck <linux@roeck-us.net>]

On Tue, Aug 15, 2023 at 12:06:50PM -0700, Nathan Chancellor wrote:
> After commit f1a43aadb5a6 ("watchdog: Enable COMPILE_TEST for more
> drivers"), it is possible to enable this driver on 32-bit architectures.
> When building for those architectures with clang, there is an error due
> to a 64-bit division in xilinx_wwdt_start():
> 
>   ERROR: modpost: "__aeabi_uldivmod" [drivers/watchdog/xilinx_wwdt.ko] undefined!
> 
> Use div_u64() to fix this, which takes a 64-bit dividend and 32-bit
> divisor. GCC likely avoids the same error due to optimizations it
> employs to transform division by a constant into other equivalent
> operations, which may be different than what is implemented in clang.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1915
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

> ---
>  drivers/watchdog/xilinx_wwdt.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/watchdog/xilinx_wwdt.c b/drivers/watchdog/xilinx_wwdt.c
> index 1d998db41533..d271e2e8d6e2 100644
> --- a/drivers/watchdog/xilinx_wwdt.c
> +++ b/drivers/watchdog/xilinx_wwdt.c
> @@ -9,6 +9,7 @@
>  #include <linux/interrupt.h>
>  #include <linux/io.h>
>  #include <linux/ioport.h>
> +#include <linux/math64.h>
>  #include <linux/mod_devicetable.h>
>  #include <linux/module.h>
>  #include <linux/platform_device.h>
> @@ -71,7 +72,7 @@ static int xilinx_wwdt_start(struct watchdog_device *wdd)
>  
>  	/* Calculate timeout count */
>  	time_out = xdev->freq * wdd->timeout;
> -	closed_timeout = (time_out * xdev->close_percent) / 100;
> +	closed_timeout = div_u64(time_out * xdev->close_percent, 100);
>  	open_timeout = time_out - closed_timeout;
>  	wdd->min_hw_heartbeat_ms = xdev->close_percent * 10 * wdd->timeout;
>  
> 
> ---
> base-commit: 8a504bd61ec7b3ddd72680e15775f2c7c0f9e894
> change-id: 20230815-watchdog-xilinx-div_u64-85c27c650493
> 
> Best regards,
> -- 
> Nathan Chancellor <nathan@kernel.org>
>