linux-kernel - Re: [PATCH 1/2] soc: qcom: stats: fix 64-bit division

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Date:   Thu, 7 Dec 2023 07:24:43 -0800
From:   Bjorn Andersson <andersson@...nel.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] soc: qcom: stats: fix 64-bit division

On Wed, Dec 06, 2023 at 01:37:06PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> Unguarded 64-bit division is not allowed on 32-bit kernels because this
> is very slow. The result of trying anyway is a link failure:
> 
> arm-linux-gnueabi-ld: drivers/soc/qcom/qcom_stats.o: in function `qcom_ddr_stats_show':
> qcom_stats.c:(.text+0x334): undefined reference to `__aeabi_uldivmod'
> 
> As this function is only used for debugging and not performance critical,
> rewrite it to use div_u64() instead. ARCH_TIMER_FREQ is a multiple of
> MSEC_PER_SEC anyway, so there is no loss in precisison.
> 
> Fixes: e84e61bdb97c ("soc: qcom: stats: Add DDR sleep stats")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

I had [1] lined up already, but hadn't pushed the branch out out... Like
your version better, so dropping mine.

[1] https://lore.kernel.org/all/20231205-qcom_stats-aeabi_uldivmod-fix-v1-1-f94ecec5e894@quicinc.com/

Thanks,
Bjorn

> ---
>  drivers/soc/qcom/qcom_stats.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/soc/qcom/qcom_stats.c b/drivers/soc/qcom/qcom_stats.c
> index 4763d62a8cb0..5ec8a754b22b 100644
> --- a/drivers/soc/qcom/qcom_stats.c
> +++ b/drivers/soc/qcom/qcom_stats.c
> @@ -221,7 +221,7 @@ static int qcom_ddr_stats_show(struct seq_file *s, void *unused)
>  
>  	for (i = 0; i < ddr.entry_count; i++) {
>  		/* Convert the period to ms */
> -		entry[i].dur = mult_frac(MSEC_PER_SEC, entry[i].dur, ARCH_TIMER_FREQ);
> +		entry[i].dur = div_u64(entry[i].dur, ARCH_TIMER_FREQ / MSEC_PER_SEC);
>  	}
>  
>  	for (i = 0; i < ddr.entry_count; i++)
> -- 
> 2.39.2
>