[PATCH] drm/panthor: Fix the CONFIG_PM=n case

[Steven Price]

On 18/03/2024 08:58, Boris Brezillon wrote:
> Putting a hard dependency on CONFIG_PM is not possible because of a
> circular dependency issue, and it's actually not desirable either. In
> order to support this use case, we forcibly resume at init time, and
> suspend at unplug time.
> 
> Reported-by: kernel test robot <lkp at intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202403031944.EOimQ8WK-lkp@intel.com/
> Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>

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

> ---
> Tested by faking CONFIG_PM=n in the driver (basically commenting
> all pm_runtime calls, and making the panthor_device_suspend/resume()
> calls unconditional in the panthor_device_unplug/init() path) since
> CONFIG_ARCH_ROCKCHIP selects CONFIG_PM. Seems to work fine, but I
> can't be 100% sure this will work correctly on a platform that has
> CONFIG_PM=n.

The same - I can't test this properly :(

Note that the other option (which AFAICT doesn't cause any problems) is
to "select PM" rather than depend on it - AIUI the 'select' dependency
is considered in the opposite direction by kconfig so won't cause the
dependency loop. Of course if there is actually anyone who has a
platform which can be built !CONFIG_PM then that won't help. But the
inability of anyone to actually properly test this configuration does
worry me a little.

Steve

> ---
>  drivers/gpu/drm/panthor/panthor_device.c | 13 +++++++++++--
>  drivers/gpu/drm/panthor/panthor_drv.c    |  4 +++-
>  2 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
> index 69deb8e17778..ba7aedbb4931 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.c
> +++ b/drivers/gpu/drm/panthor/panthor_device.c
> @@ -87,6 +87,10 @@ void panthor_device_unplug(struct panthor_device *ptdev)
>  	pm_runtime_dont_use_autosuspend(ptdev->base.dev);
>  	pm_runtime_put_sync_suspend(ptdev->base.dev);
>  
> +	/* If PM is disabled, we need to call the suspend handler manually. */
> +	if (!IS_ENABLED(CONFIG_PM))
> +		panthor_device_suspend(ptdev->base.dev);
> +
>  	/* Report the unplug operation as done to unblock concurrent
>  	 * panthor_device_unplug() callers.
>  	 */
> @@ -218,6 +222,13 @@ int panthor_device_init(struct panthor_device *ptdev)
>  	if (ret)
>  		return ret;
>  
> +	/* If PM is disabled, we need to call panthor_device_resume() manually. */
> +	if (!IS_ENABLED(CONFIG_PM)) {
> +		ret = panthor_device_resume(ptdev->base.dev);
> +		if (ret)
> +			return ret;
> +	}
> +
>  	ret = panthor_gpu_init(ptdev);
>  	if (ret)
>  		goto err_rpm_put;
> @@ -402,7 +413,6 @@ int panthor_device_mmap_io(struct panthor_device *ptdev, struct vm_area_struct *
>  	return 0;
>  }
>  
> -#ifdef CONFIG_PM
>  int panthor_device_resume(struct device *dev)
>  {
>  	struct panthor_device *ptdev = dev_get_drvdata(dev);
> @@ -547,4 +557,3 @@ int panthor_device_suspend(struct device *dev)
>  	mutex_unlock(&ptdev->pm.mmio_lock);
>  	return ret;
>  }
> -#endif
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> index ff484506229f..2ea6a9f436db 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -1407,17 +1407,19 @@ static const struct of_device_id dt_match[] = {
>  };
>  MODULE_DEVICE_TABLE(of, dt_match);
>  
> +#ifdef CONFIG_PM
>  static DEFINE_RUNTIME_DEV_PM_OPS(panthor_pm_ops,
>  				 panthor_device_suspend,
>  				 panthor_device_resume,
>  				 NULL);
> +#endif
>  
>  static struct platform_driver panthor_driver = {
>  	.probe = panthor_probe,
>  	.remove_new = panthor_remove,
>  	.driver = {
>  		.name = "panthor",
> -		.pm = &panthor_pm_ops,
> +		.pm = pm_ptr(&panthor_pm_ops),
>  		.of_match_table = dt_match,
>  	},
>  };