[PATCH v4] vfio: platform: Fix using devices in PM Domains

[Geert Uytterhoeven <geert+renesas@glider.be>]

If a device is part of a PM Domain (e.g. power and/or clock domain), its
power state is managed using Runtime PM.  Without Runtime PM, the device
may not be powered up or clocked, causing subtle failures, crashes, or
system lock-ups when the device is accessed by the guest.

Fix this by adding Runtime PM support, powering the device when the VFIO
device is opened by the guest.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
---
Against linux-vfio/next

v4:
  - Keep device powered while issuing reset,

v3:
  - Drop controversial note about unsafeness of exporting fine-grained
    power management from host to guest,

v2:
  - Improve wording,
  - Add Reviewed-by.
---
 drivers/vfio/platform/vfio_platform_common.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/vfio/platform/vfio_platform_common.c b/drivers/vfio/platform/vfio_platform_common.c
index b60bb5326668498c..c0cd824be2b767be 100644
--- a/drivers/vfio/platform/vfio_platform_common.c
+++ b/drivers/vfio/platform/vfio_platform_common.c
@@ -17,6 +17,7 @@
 #include <linux/iommu.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/pm_runtime.h>
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/uaccess.h>
@@ -239,6 +240,7 @@ static void vfio_platform_release(void *device_data)
 				 ret, extra_dbg ? extra_dbg : "");
 			WARN_ON(1);
 		}
+		pm_runtime_put(vdev->device);
 		vfio_platform_regions_cleanup(vdev);
 		vfio_platform_irq_cleanup(vdev);
 	}
@@ -269,6 +271,10 @@ static int vfio_platform_open(void *device_data)
 		if (ret)
 			goto err_irq;
 
+		ret = pm_runtime_get_sync(vdev->device);
+		if (ret < 0)
+			goto err_pm;
+
 		ret = vfio_platform_call_reset(vdev, &extra_dbg);
 		if (ret && vdev->reset_required) {
 			dev_warn(vdev->device, "reset driver is required and reset call failed in open (%d) %s\n",
@@ -283,6 +289,8 @@ static int vfio_platform_open(void *device_data)
 	return 0;
 
 err_rst:
+	pm_runtime_put(vdev->device);
+err_pm:
 	vfio_platform_irq_cleanup(vdev);
 err_irq:
 	vfio_platform_regions_cleanup(vdev);
@@ -690,6 +698,7 @@ int vfio_platform_probe_common(struct vfio_platform_device *vdev,
 
 	mutex_init(&vdev->igate);
 
+	pm_runtime_enable(vdev->device);
 	return 0;
 
 put_iommu:
@@ -707,6 +716,7 @@ struct vfio_platform_device *vfio_platform_remove_common(struct device *dev)
 	vdev = vfio_del_group_dev(dev);
 
 	if (vdev) {
+		pm_runtime_disable(vdev->device);
 		vfio_platform_put_reset(vdev);
 		vfio_iommu_group_put(dev->iommu_group, dev);
 	}
-- 
2.7.4