Re: [PATCH v12 06/15] drm/panfrost: Fix PM refcnt and autosuspend issues at device probe/remove

[Steven Price <steven.price@arm.com>]

On 29/09/2026 04:44, Adrián Larumbe wrote:
> During device probe(), failure to do a PM get() will leave the usage_count
> set to 0, which is the value assigned at device creation time. That means
> when the autosuspend delay expires, runtime suspend callback won't be
> invoked, so the device will remain powered on forever.
> 
> On top of that, failure to call PM put() during device unplug means
> Panfrost device's PM usage_count increases monotonically for every new
> module reload.
> 
> The outcome of both of the above meant that:
> 
> - Devfreq OPP transition notifications would be printed all the time,
>   even when no jobs are being submitted. This quickly fills the kernel
>   ring buffer with junk.
> - Because MMU interrupts are only enabled when the device is reset,
>   the very first job targeting the tiler heap BO after device probe()
>   would always time out, since the driver's PM runtime resume callback
>   would not be invoked.
> 
> To fix the above:
> - Manually adjust the PM refcnt at device probe and removal time.
> - Ensure pm_runtime_dont_use_autosuspend is called in the wind-down path.
> - Call pm_runtime_put_autosuspend() when device is ready to accept jobs
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> Fixes: 635430797d3f ("drm/panfrost: Rework runtime PM initialization")
> Fixes: 876b15d2c88d ("drm/panfrost: Fix module unload")

Reviewed-by: Steven Price <steven.price@arm.com>

> ---
>  drivers/gpu/drm/panfrost/panfrost_drv.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> index 55fc22e8d4d4..907d4a14a0b5 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> @@ -852,6 +852,11 @@ static int panfrost_probe(struct platform_device *pdev)
>  		goto err_out0;
>  	}
>  
> +	/* The reason we must manually set the PM status and usage counter is
> +	 * we have just powered the device up but did not go through the PM
> +	 * runtime resume callback, so we need to update these ourselves.
> +	 */
> +	pm_runtime_get_noresume(pfdev->base.dev);
>  	pm_runtime_set_active(pfdev->base.dev);
>  	pm_runtime_mark_last_busy(pfdev->base.dev);
>  	pm_runtime_enable(pfdev->base.dev);
> @@ -866,13 +871,16 @@ static int panfrost_probe(struct platform_device *pdev)
>  	if (err < 0)
>  		goto err_out1;
>  
> +	pm_runtime_put_autosuspend(pfdev->base.dev);
>  
>  	return 0;
>  
>  err_out1:
> +	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);
>  err_out0:
>  	return err;
>  }
> @@ -884,9 +892,12 @@ static void panfrost_remove(struct platform_device *pdev)
>  	drm_dev_unregister(&pfdev->base);
>  
>  	pm_runtime_get_sync(pfdev->base.dev);
> +	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);
> +
>  }
>  
>  static ssize_t profiling_show(struct device *dev,
>