drm/tegra: Do not implement runtime PM

The Tegra DRM driver heavily relies on the implementations for runtime
suspend/resume to be called at specific times. Unfortunately, there are
some cases where that doesn't work. One example is if the user disables
runtime PM for a given subdevice. Another example is that the PM core
acquires a reference to runtime PM during system sleep, effectively
preventing devices from going into low power modes. This is intentional
to avoid nasty race conditions, but it also causes system sleep to not
function properly on all Tegra systems.

Fix this by not implementing runtime PM at all. Instead, a minimal,
reference-counted suspend/resume infrastructure is added to the host1x
bus. This has the benefit that it can be used regardless of the system
power state (or any transitions we might be in), or whether or not the
user allows runtime PM.

Atomic modesetting guarantees that these functions will end up being
called at the right point in time, so the pitfalls for the more generic
runtime PM do not apply here.

Signed-off-by: Thierry Reding <treding@nvidia.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/host1x.h b/include/linux/host1x.h
index b673d6198e05..325dabe4dd36 100644
--- a/include/linux/host1x.h
+++ b/include/linux/host1x.h
@@ -24,10 +24,14 @@ struct iommu_group;
  * struct host1x_client_ops - host1x client operations
  * @init: host1x client initialization code
  * @exit: host1x client tear down code
+ * @suspend: host1x client suspend code
+ * @resume: host1x client resume code
  */
 struct host1x_client_ops {
 	int (*init)(struct host1x_client *client);
 	int (*exit)(struct host1x_client *client);
+	int (*suspend)(struct host1x_client *client);
+	int (*resume)(struct host1x_client *client);
 };
 
 /**
@@ -55,6 +59,10 @@ struct host1x_client {
 
 	struct host1x_syncpt **syncpts;
 	unsigned int num_syncpts;
+
+	struct host1x_client *parent;
+	unsigned int usecount;
+	struct mutex lock;
 };
 
 /*
@@ -322,6 +330,9 @@ int host1x_device_exit(struct host1x_device *device);
 int host1x_client_register(struct host1x_client *client);
 int host1x_client_unregister(struct host1x_client *client);
 
+int host1x_client_suspend(struct host1x_client *client);
+int host1x_client_resume(struct host1x_client *client);
+
 struct tegra_mipi_device;
 
 struct tegra_mipi_device *tegra_mipi_request(struct device *device);