PM QoS: Implement per-device PM QoS constraints

Implement the per-device PM QoS constraints by creating a device
PM QoS API, which calls the PM QoS constraints management core code.

The per-device latency constraints data strctures are stored
in the device dev_pm_info struct.

The device PM code calls the init and destroy of the per-device constraints
data struct in order to support the dynamic insertion and removal of the
devices in the system.

To minimize the data usage by the per-device constraints, the data struct
is only allocated at the first call to dev_pm_qos_add_request.
The data is later free'd when the device is removed from the system.
A global mutex protects the constraints users from the data being
allocated and free'd.

Signed-off-by: Jean Pihet <j-pihet@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

1 files changed, 338 insertions, 0 deletions

diff --git a/drivers/base/power/qos.c b/drivers/base/power/qos.c
new file mode 100644
index 000000000000..cc4c541398aa
--- /dev/null
+++ b/drivers/base/power/qos.c
@@ -0,0 +1,338 @@
+/*
+ * Devices PM QoS constraints management
+ *
+ * Copyright (C) 2011 Texas Instruments, Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ *
+ * This module exposes the interface to kernel space for specifying
+ * per-device PM QoS dependencies. It provides infrastructure for registration
+ * of:
+ *
+ * Dependents on a QoS value : register requests
+ * Watchers of QoS value : get notified when target QoS value changes
+ *
+ * This QoS design is best effort based. Dependents register their QoS needs.
+ * Watchers register to keep track of the current QoS needs of the system.
+ *
+ * Note about the per-device constraint data struct allocation:
+ * . The per-device constraints data struct ptr is tored into the device
+ *    dev_pm_info.
+ * . To minimize the data usage by the per-device constraints, the data struct
+ *   is only allocated at the first call to dev_pm_qos_add_request.
+ * . The data is later free'd when the device is removed from the system.
+ * . The constraints_state variable from dev_pm_info tracks the data struct
+ *    allocation state:
+ *    DEV_PM_QOS_NO_DEVICE: No device present or device removed, no data
+ *     allocated,
+ *    DEV_PM_QOS_DEVICE_PRESENT: Device present, data not allocated and will be
+ *     allocated at the first call to dev_pm_qos_add_request,
+ *    DEV_PM_QOS_ALLOCATED: Device present, data allocated. The per-device
+ *     PM QoS constraints framework is operational and constraints can be
+ *     added, updated or removed using the dev_pm_qos_* API.
+ *  . A global mutex protects the constraints users from the data being
+ *     allocated and free'd.
+ */
+
+#include <linux/pm_qos.h>
+#include <linux/spinlock.h>
+#include <linux/slab.h>
+#include <linux/device.h>
+#include <linux/mutex.h>
+
+
+static DEFINE_MUTEX(dev_pm_qos_mtx);
+
+/*
+ * dev_pm_qos_constraints_allocate
+ * @dev: device to allocate data for
+ *
+ * Called at the first call to add_request, for constraint data allocation
+ * Must be called with the dev_pm_qos_mtx mutex held
+ */
+static int dev_pm_qos_constraints_allocate(struct device *dev)
+{
+        struct pm_qos_constraints *c;
+        struct blocking_notifier_head *n;
+
+        c = kzalloc(sizeof(*c), GFP_KERNEL);
+        if (!c)
+                return -ENOMEM;
+
+        n = kzalloc(sizeof(*n), GFP_KERNEL);
+        if (!n) {
+                kfree(c);
+                return -ENOMEM;
+        }
+        BLOCKING_INIT_NOTIFIER_HEAD(n);
+
+        dev->power.constraints = c;
+        plist_head_init(&dev->power.constraints->list);
+        dev->power.constraints->target_value = PM_QOS_DEV_LAT_DEFAULT_VALUE;
+        dev->power.constraints->default_value = PM_QOS_DEV_LAT_DEFAULT_VALUE;
+        dev->power.constraints->type = PM_QOS_MIN;
+        dev->power.constraints->notifiers = n;
+        dev->power.constraints_state = DEV_PM_QOS_ALLOCATED;
+
+        return 0;
+}
+
+/**
+ * dev_pm_qos_constraints_init
+ * @dev: target device
+ *
+ * Called from the device PM subsystem at device insertion
+ */
+void dev_pm_qos_constraints_init(struct device *dev)
+{
+        mutex_lock(&dev_pm_qos_mtx);
+        dev->power.constraints_state = DEV_PM_QOS_DEVICE_PRESENT;
+        mutex_unlock(&dev_pm_qos_mtx);
+}
+
+/**
+ * dev_pm_qos_constraints_destroy
+ * @dev: target device
+ *
+ * Called from the device PM subsystem at device removal
+ */
+void dev_pm_qos_constraints_destroy(struct device *dev)
+{
+        struct dev_pm_qos_request *req, *tmp;
+
+        mutex_lock(&dev_pm_qos_mtx);
+
+        if (dev->power.constraints_state == DEV_PM_QOS_ALLOCATED) {
+                /* Flush the constraints list for the device */
+                plist_for_each_entry_safe(req, tmp,
+                                          &dev->power.constraints->list,
+                                          node) {
+                        /*
+                         * Update constraints list and call the per-device
+                         * callbacks if needed
+                         */
+                        pm_qos_update_target(req->dev->power.constraints,
+                                           &req->node, PM_QOS_REMOVE_REQ,
+                                           PM_QOS_DEFAULT_VALUE);
+                        memset(req, 0, sizeof(*req));
+                }
+
+                kfree(dev->power.constraints->notifiers);
+                kfree(dev->power.constraints);
+                dev->power.constraints = NULL;
+        }
+        dev->power.constraints_state = DEV_PM_QOS_NO_DEVICE;
+
+        mutex_unlock(&dev_pm_qos_mtx);
+}
+
+/**
+ * dev_pm_qos_add_request - inserts new qos request into the list
+ * @dev: target device for the constraint
+ * @req: pointer to a preallocated handle
+ * @value: defines the qos request
+ *
+ * This function inserts a new entry in the device constraints list of
+ * requested qos performance characteristics. It recomputes the aggregate
+ * QoS expectations of parameters and initializes the dev_pm_qos_request
+ * handle.  Caller needs to save this handle for later use in updates and
+ * removal.
+ *
+ * Returns 1 if the aggregated constraint value has changed,
+ * 0 if the aggregated constraint value has not changed,
+ * -EINVAL in case of wrong parameters, -ENODEV if the device has been
+ * removed from the system
+ */
+int dev_pm_qos_add_request(struct device *dev, struct dev_pm_qos_request *req,
+                            s32 value)
+{
+        int ret = 0;
+
+        if (!dev || !req) /*guard against callers passing in null */
+                return -EINVAL;
+
+        if (dev_pm_qos_request_active(req)) {
+                WARN(1, KERN_ERR "dev_pm_qos_add_request() called for already "
+                        "added request\n");
+                return -EINVAL;
+        }
+
+        mutex_lock(&dev_pm_qos_mtx);
+        req->dev = dev;
+
+        /* Return if the device has been removed */
+        if (req->dev->power.constraints_state == DEV_PM_QOS_NO_DEVICE) {
+                ret = -ENODEV;
+                goto out;
+        }
+
+        /*
+         * Allocate the constraints data on the first call to add_request,
+         * i.e. only if the data is not already allocated and if the device has
+         * not been removed
+         */
+        if (dev->power.constraints_state == DEV_PM_QOS_DEVICE_PRESENT)
+                ret = dev_pm_qos_constraints_allocate(dev);
+
+        if (!ret)
+                ret = pm_qos_update_target(dev->power.constraints, &req->node,
+                                           PM_QOS_ADD_REQ, value);
+
+out:
+        mutex_unlock(&dev_pm_qos_mtx);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(dev_pm_qos_add_request);
+
+/**
+ * dev_pm_qos_update_request - modifies an existing qos request
+ * @req : handle to list element holding a dev_pm_qos request to use
+ * @new_value: defines the qos request
+ *
+ * Updates an existing dev PM qos request along with updating the
+ * target value.
+ *
+ * Attempts are made to make this code callable on hot code paths.
+ *
+ * Returns 1 if the aggregated constraint value has changed,
+ * 0 if the aggregated constraint value has not changed,
+ * -EINVAL in case of wrong parameters, -ENODEV if the device has been
+ * removed from the system
+ */
+int dev_pm_qos_update_request(struct dev_pm_qos_request *req,
+                              s32 new_value)
+{
+        int ret = 0;
+
+        if (!req) /*guard against callers passing in null */
+                return -EINVAL;
+
+        if (!dev_pm_qos_request_active(req)) {
+                WARN(1, KERN_ERR "dev_pm_qos_update_request() called for "
+                        "unknown object\n");
+                return -EINVAL;
+        }
+
+        mutex_lock(&dev_pm_qos_mtx);
+
+        if (req->dev->power.constraints_state == DEV_PM_QOS_ALLOCATED) {
+                if (new_value != req->node.prio)
+                        ret = pm_qos_update_target(req->dev->power.constraints,
+                                                   &req->node,
+                                                   PM_QOS_UPDATE_REQ,
+                                                   new_value);
+        } else {
+                /* Return if the device has been removed */
+                ret = -ENODEV;
+        }
+
+        mutex_unlock(&dev_pm_qos_mtx);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(dev_pm_qos_update_request);
+
+/**
+ * dev_pm_qos_remove_request - modifies an existing qos request
+ * @req: handle to request list element
+ *
+ * Will remove pm qos request from the list of constraints and
+ * recompute the current target value. Call this on slow code paths.
+ *
+ * Returns 1 if the aggregated constraint value has changed,
+ * 0 if the aggregated constraint value has not changed,
+ * -EINVAL in case of wrong parameters, -ENODEV if the device has been
+ * removed from the system
+ */
+int dev_pm_qos_remove_request(struct dev_pm_qos_request *req)
+{
+        int ret = 0;
+
+        if (!req) /*guard against callers passing in null */
+                return -EINVAL;
+
+        if (!dev_pm_qos_request_active(req)) {
+                WARN(1, KERN_ERR "dev_pm_qos_remove_request() called for "
+                        "unknown object\n");
+                return -EINVAL;
+        }
+
+        mutex_lock(&dev_pm_qos_mtx);
+
+        if (req->dev->power.constraints_state == DEV_PM_QOS_ALLOCATED) {
+                ret = pm_qos_update_target(req->dev->power.constraints,
+                                           &req->node, PM_QOS_REMOVE_REQ,
+                                           PM_QOS_DEFAULT_VALUE);
+                memset(req, 0, sizeof(*req));
+        } else {
+                /* Return if the device has been removed */
+                ret = -ENODEV;
+        }
+
+        mutex_unlock(&dev_pm_qos_mtx);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(dev_pm_qos_remove_request);
+
+/**
+ * dev_pm_qos_add_notifier - sets notification entry for changes to target value
+ * of per-device PM QoS constraints
+ *
+ * @dev: target device for the constraint
+ * @notifier: notifier block managed by caller.
+ *
+ * Will register the notifier into a notification chain that gets called
+ * upon changes to the target value for the device.
+ */
+int dev_pm_qos_add_notifier(struct device *dev, struct notifier_block *notifier)
+{
+        int retval = 0;
+
+        mutex_lock(&dev_pm_qos_mtx);
+
+        /* Silently return if the device has been removed */
+        if (dev->power.constraints_state != DEV_PM_QOS_ALLOCATED)
+                goto out;
+
+        retval = blocking_notifier_chain_register(
+                        dev->power.constraints->notifiers,
+                        notifier);
+
+out:
+        mutex_unlock(&dev_pm_qos_mtx);
+        return retval;
+}
+EXPORT_SYMBOL_GPL(dev_pm_qos_add_notifier);
+
+/**
+ * dev_pm_qos_remove_notifier - deletes notification for changes to target value
+ * of per-device PM QoS constraints
+ *
+ * @dev: target device for the constraint
+ * @notifier: notifier block to be removed.
+ *
+ * Will remove the notifier from the notification chain that gets called
+ * upon changes to the target value.
+ */
+int dev_pm_qos_remove_notifier(struct device *dev,
+                               struct notifier_block *notifier)
+{
+        int retval = 0;
+
+        mutex_lock(&dev_pm_qos_mtx);
+
+        /* Silently return if the device has been removed */
+        if (dev->power.constraints_state != DEV_PM_QOS_ALLOCATED)
+                goto out;
+
+        retval = blocking_notifier_chain_unregister(
+                        dev->power.constraints->notifiers,
+                        notifier);
+
+out:
+        mutex_unlock(&dev_pm_qos_mtx);
+        return retval;
+}
+EXPORT_SYMBOL_GPL(dev_pm_qos_remove_notifier);