Re: [PATCH v4 02/13] drm/panfrost: Prevent division by 0

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Integer overflow in devfreq load calculation on 32-bit architectures
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--- Patch [2]: [PATCH v4 02/13] drm/panfrost: Prevent division by 0 ---
commit 1a597fba6ac1a7783fb883935107fe50d2c19cfa
Author: Adrián Larumbe <adrian.larumbe@collabora.com>

drm/panfrost: Prevent division by 0

This commit modifies the devfreq status calculation to prevent a division
by zero when the total device time is less than 100 ns. It updates the
debug logging divisor and rearranges the operands.

Closes: https://gitlab.freedesktop.org/panfrost/linux/-/work_items/88

> diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.c b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> index b51c307788110..0fe81d259274e 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> @@ -78,7 +78,7 @@ static int panfrost_devfreq_get_dev_status(struct device *dev,
>  
>  	dev_dbg(pfdev->base.dev, "busy %lu total %lu %lu %% freq %lu MHz\n",
>  		status->busy_time, status->total_time,
> -		status->busy_time / (status->total_time / 100),
> +		status->busy_time * 100 / MAX(status->total_time, 1),

[Severity: Medium]
Will this cause an integer overflow on 32-bit architectures?

In panfrost_devfreq_get_dev_status(), status->busy_time is an unsigned
long, which is 32 bits on platforms like ARM32.

Since the Panfrost devfreq polling interval is 50ms, a fully busy GPU will
have a status->busy_time around 50,000,000 ns. Multiplying 50,000,000 by
100 yields 5,000,000,000, which overflows the 32-bit ULONG_MAX
(4,294,967,295) and wraps around to 705,032,704.

When this is divided by 50,000,000, it results in 14% instead of the
expected 100%.

Could this be calculated using a 64-bit type or a div-related macro to
prevent the debug log from reporting incorrect load percentages on heavily
loaded 32-bit systems?

>  		status->current_frequency / 1000 / 1000);
>  
>  	return 0;

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Sashiko AI review · https://sashiko.dev/#/patchset/20260729-claude-fixes-v4-0-01968f2ec77a@collabora.com?part=2