[PATCH v5 1/4] drm: Introduce device wedged event

[Raag Jadav]

Introduce device wedged event, which will notify userspace of wedged
(hanged/unusable) state of the DRM device through a uevent. This is
useful especially in cases where the device is no longer operating as
expected and has become unrecoverable from driver context.

Purpose of this implementation is to provide drivers a way to recover
through userspace intervention. Different drivers may have different
ideas of a "wedged device" depending on their hardware implementation,
and hence the vendor agnostic nature of the event. It is upto the drivers
to decide when they see the need for recovery and how they want to recover
from the available methods.

Current implementation defines three recovery methods, out of which,
drivers can choose to support any one or multiple of them. Preferred
recovery method will be sent in the uevent environment as WEDGED=<method>.
Userspace consumers (sysadmin) can define udev rules to parse this event
and take respective action to recover the device.

 Method    | Consumer expectations
-----------|-----------------------------------
 rebind    | unbind + rebind driver
 bus-reset | unbind + reset bus device + rebind
 reboot    | reboot system

v4: s/drm_dev_wedged/drm_dev_wedged_event
    Use drm_info() (Jani)
    Kernel doc adjustment (Aravind)
v5: Send recovery method with uevent (Lina)

Signed-off-by: Raag Jadav <raag.jadav at intel.com>
---
 drivers/gpu/drm/drm_drv.c | 37 +++++++++++++++++++++++++++++++++++++
 include/drm/drm_device.h  | 24 ++++++++++++++++++++++++
 include/drm/drm_drv.h     |  1 +
 3 files changed, 62 insertions(+)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index ac30b0ec9d93..1e850a9f608d 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -497,6 +497,43 @@ void drm_dev_unplug(struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_dev_unplug);
 
+const char *const wedge_recovery_opts[] = {
+	[DRM_WEDGE_RECOVERY_REBIND] = "rebind",
+	[DRM_WEDGE_RECOVERY_BUS_RESET] = "bus-reset",
+	[DRM_WEDGE_RECOVERY_REBOOT] = "reboot",
+};
+
+/**
+ * drm_dev_wedged_event - generate a device wedged uevent
+ * @dev: DRM device
+ * @method: method to be used for recovery
+ *
+ * This generates a device wedged uevent for the DRM device specified by @dev.
+ * Recovery @method from wedge_recovery_opts[] (if supprted by the device) is
+ * sent in the uevent environment as WEDGED=<method>, on the basis of which,
+ * userspace may take respective action to recover the device.
+ *
+ * Returns: 0 on success, or negative error code otherwise.
+ */
+int drm_dev_wedged_event(struct drm_device *dev, enum wedge_recovery_method method)
+{
+	char event_string[32] = "WEDGED=";
+	char *envp[] = { event_string, NULL };
+	bool supported;
+
+	supported = test_bit(method, &dev->wedge_recovery);
+	if (unlikely(!supported)) {
+		drm_err(dev, "device wedged, recovery method not supported\n");
+		return -EOPNOTSUPP;
+	}
+
+	strcat(event_string, wedge_recovery_opts[method]);
+
+	drm_info(dev, "device wedged, generating uevent\n");
+	return kobject_uevent_env(&dev->primary->kdev->kobj, KOBJ_CHANGE, envp);
+}
+EXPORT_SYMBOL(drm_dev_wedged_event);
+
 /*
  * DRM internal mount
  * We want to be able to allocate our own "struct address_space" to control
diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h
index c91f87b5242d..e4f32967b5ae 100644
--- a/include/drm/drm_device.h
+++ b/include/drm/drm_device.h
@@ -40,6 +40,27 @@ enum switch_power_state {
 	DRM_SWITCH_POWER_DYNAMIC_OFF = 3,
 };
 
+/**
+ * enum wedge_recovery_method - Recovery method for wedged device in order
+ * of severity. To be set as bit fields in drm_device.wedge_recovery variable.
+ * Drivers can choose to support any one or multiple of them depending on their
+ * needs.
+ */
+
+enum wedge_recovery_method {
+	/** @DRM_WEDGE_RECOVERY_REBIND: unbind + rebind driver */
+	DRM_WEDGE_RECOVERY_REBIND = 0,
+
+	/** @DRM_WEDGE_RECOVERY_BUS_RESET: unbind + reset bus device + rebind */
+	DRM_WEDGE_RECOVERY_BUS_RESET = 1,
+
+	/** @DRM_WEDGE_RECOVERY_REBOOT: reboot system */
+	DRM_WEDGE_RECOVERY_REBOOT = 2,
+
+	/** @DRM_WEDGE_RECOVERY_MAX: for bounds checking, do not use */
+	DRM_WEDGE_RECOVERY_MAX = 3,
+};
+
 /**
  * struct drm_device - DRM device structure
  *
@@ -317,6 +338,9 @@ struct drm_device {
 	 * Root directory for debugfs files.
 	 */
 	struct dentry *debugfs_root;
+
+	/** @wedge_recovery: Supported recovery methods for wedged device */
+	unsigned long wedge_recovery;
 };
 
 #endif
diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
index 02ea4e3248fd..6e02187f1f6c 100644
--- a/include/drm/drm_drv.h
+++ b/include/drm/drm_drv.h
@@ -461,6 +461,7 @@ void drm_put_dev(struct drm_device *dev);
 bool drm_dev_enter(struct drm_device *dev, int *idx);
 void drm_dev_exit(int idx);
 void drm_dev_unplug(struct drm_device *dev);
+int drm_dev_wedged_event(struct drm_device *dev, enum wedge_recovery_method method);
 
 /**
  * drm_dev_is_unplugged - is a DRM device unplugged
-- 
2.34.1