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

[Boris Brezillon <boris.brezillon@collabora.com>]

On Mon, 18 Mar 2024 12:18:53 +0000
Robin Murphy <robin.murphy@arm.com> wrote:

> On 18/03/2024 8:58 am, 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@intel.com>
> > Closes: https://lore.kernel.org/oe-kbuild-all/202403031944.EOimQ8WK-lkp@intel.com/
> > Signed-off-by: Boris Brezillon <boris.brezillon@collabora.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.
> > ---
> >   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  
> 
> This #ifdef isn't necessary, and in fact will break the !PM build - 
> pm_ptr() already takes care of allowing the compiler to optimise out the 
> ops structure itself without any further annotations.

Oops, I forgot how pm_ptr() was working (I thought it had 2
definitions, one for the PM case and another for the !PM one).

> 
> Thanks,
> Robin.
> 
> >   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,
> >   	},
> >   };