Re: [PATCH v2 10/28] drm/panthor: Skip devfreq when no OPP table is present

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Medium] drm/panthor: panthor_devfreq_init() leaves fast_rate at 0 on
  early return
--

commit f3bfa3d1d539b4b1bfaa2d96f490e98746dad160
Author: Karunika Choo <karunika.choo@arm.com>

drm/panthor: Skip devfreq when no OPP table is present

This commit skips devfreq initialization on Mali v15 AM systems when no OPP
table is present, guards the devfreq helpers against a NULL devfreq
instance, and falls back to clk_get_rate() when querying the current
frequency without devfreq.

> diff --git a/drivers/gpu/drm/panthor/panthor_devfreq.c b/drivers/gpu/drm/panthor/panthor_devfreq.c
> index 2249b41ca4afe..d1814b5197221 100644
> --- a/drivers/gpu/drm/panthor/panthor_devfreq.c
> +++ b/drivers/gpu/drm/panthor/panthor_devfreq.c

[ ... ]

> @@ -164,6 +165,19 @@ int panthor_devfreq_init(struct panthor_device *ptdev)
>  	 */
>  	table = dev_pm_opp_get_opp_table(dev);
>  	if (IS_ERR_OR_NULL(table)) {
> +		/*
> +		 * On v15 GPUs, frequency scaling is handled outside of panthor
> +		 * by the AM_GOVERNOR block, so the GPU DT node may not provide
> +		 * an OPP table. In such cases, do not initialize devfreq for
> +		 * panthor.
> +		 */
> +		if (panthor_hw_is_gen5_am(ptdev->base.dev) &&
> +		    PTR_ERR(table) == -ENODEV) {
> +			drmm_kfree(&ptdev->base, pdevfreq);
> +			ptdev->devfreq = NULL;
> +			return 0;
> +		}

[Severity: Medium]
As reported by Steven Price on RFC [1], does returning early here leave
ptdev->fast_rate at 0?  ptdev->fast_rate is only populated later in
panthor_devfreq_init() via dev_pm_opp_find_freq_floor(), and
panthor_gpu_show_fdinfo() unconditionally prints it:

drivers/gpu/drm/panthor/panthor_drv.c:panthor_gpu_show_fdinfo() {
	...
	drm_printf(p, "drm-maxfreq-panthor:\t%lu Hz\n", ptdev->fast_rate);
	drm_printf(p, "drm-curfreq-panthor:\t%lu Hz\n",
		   panthor_devfreq_get_freq(ptdev));
}

On v15 AM systems without an OPP table, reading fdinfo will report
"drm-maxfreq-panthor: 0 Hz" alongside a non-zero current frequency,
breaking userspace GPU utilization calculations that divide cycle counts
by drm-maxfreq-panthor.

[1] https://lore.kernel.org/r/dc038a81-3c59-49d5-ab8a-29202c7ce935@arm.com

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261110153907.3241978-1-karunika.choo@arm.com?part=10