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

[Robin Murphy]

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 <l...@intel.com>
Closes: 
https://lore.kernel.org/oe-kbuild-all/202403031944.eoimq8wk-...@intel.com/
Signed-off-by: Boris Brezillon <boris.brezil...@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.

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,
        },
  };