Re: [PATCH v14 06/15] drm/panfrost: Fix PM refcnt and autosuspend issues at device probe/remove

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] drm/panfrost: fatal bus fault on pm_runtime_get_sync() failure during teardown
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commit b75b37397a751cf9b55bbc2c3a99131de6b299ec
Author: Adrián Larumbe <adrian.larumbe@collabora.com>

drm/panfrost: Fix PM refcnt and autosuspend issues at device probe/remove

This commit manually adjusts the PM usage counter during device probe and
removal to ensure autosuspend works correctly. It calls
pm_runtime_dont_use_autosuspend() in the wind-down path to fix devfreq
spam and job timeouts.

> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
[ ... ]
> @@ -884,9 +892,12 @@ static void panfrost_remove(struct platform_device *pdev)
>  	drm_dev_unregister(&pfdev->base);
>  
>  	pm_runtime_get_sync(pfdev->base.dev);

[Severity: High]
If pm_runtime_get_sync() fails here, could this lead to a fatal bus fault?

In panfrost_remove() in drivers/gpu/drm/panfrost/panfrost_drv.c, the return
value of pm_runtime_get_sync() is ignored. If the resume operation fails,
the device remains in a suspended state with its clocks and power domains
disabled.

The code then unconditionally calls panfrost_device_fini(), which executes
hardware teardown functions like panfrost_jm_fini(), panfrost_mmu_fini(),
and panfrost_gpu_fini(). These functions read and write MMIO registers.

Accessing unclocked or unpowered MMIO registers on ARM SoC architectures
triggers a fatal synchronous external abort (SError) or data abort, which
brings down the entire system. Should hardware register accesses be
explicitly skipped if power could not be restored?

> +	pm_runtime_dont_use_autosuspend(pfdev->base.dev);
>  	pm_runtime_disable(pfdev->base.dev);
>  	panfrost_device_fini(pfdev);
>  	pm_runtime_set_suspended(pfdev->base.dev);
> +	pm_runtime_put_noidle(pfdev->base.dev);
> +
>  }

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Sashiko AI review · https://sashiko.dev/#/patchset/20261009-claude-fixes-v14-0-cb743b3b973b@collabora.com?part=6