[PATCH v8 06/16] drm/panfrost: Fix PM refcnt and autosuspend issues at device probe/remove

[Adrián Larumbe]

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
- Move pm_runtime_set_suspended() before panfrost_device_fini() so that
  resource unwinding happens in the opposite order as initialisation.

Signed-off-by: Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx>
Fixes: 635430797d3f ("drm/panfrost: Rework runtime PM initialization")
Fixes: 876b15d2c88d ("drm/panfrost: Fix module unload")
---
 drivers/gpu/drm/panfrost/panfrost_drv.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
index 55fc22e8d4d4..a3eff77add55 100644
--- a/drivers/gpu/drm/panfrost/panfrost_drv.c
+++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
@@ -854,6 +854,7 @@ static int panfrost_probe(struct platform_device *pdev)
 
 	pm_runtime_set_active(pfdev->base.dev);
 	pm_runtime_mark_last_busy(pfdev->base.dev);
+	pm_runtime_get_noresume(pfdev->base.dev);
 	pm_runtime_enable(pfdev->base.dev);
 	pm_runtime_set_autosuspend_delay(pfdev->base.dev, 50); /* ~3 frames */
 	pm_runtime_use_autosuspend(pfdev->base.dev);
@@ -866,13 +867,16 @@ 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_put_noidle(pfdev->base.dev);
 	pm_runtime_set_suspended(pfdev->base.dev);
+	panfrost_device_fini(pfdev);
 err_out0:
 	return err;
 }
@@ -884,9 +888,11 @@ 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_put_noidle(pfdev->base.dev);
 	pm_runtime_disable(pfdev->base.dev);
-	panfrost_device_fini(pfdev);
 	pm_runtime_set_suspended(pfdev->base.dev);
+	panfrost_device_fini(pfdev);
 }
 
 static ssize_t profiling_show(struct device *dev,

-- 
2.55.0