drivers/base/power/qos.c

   1 /*
   2  * Devices PM QoS constraints management
   3  *
   4  * Copyright (C) 2011 Texas Instruments, Inc.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  *
  10  *
  11  * This module exposes the interface to kernel space for specifying
  12  * per-device PM QoS dependencies. It provides infrastructure for registration
  13  * of:
  14  *
  15  * Dependents on a QoS value : register requests
  16  * Watchers of QoS value : get notified when target QoS value changes
  17  *
  18  * This QoS design is best effort based. Dependents register their QoS needs.
  19  * Watchers register to keep track of the current QoS needs of the system.
  20  *
  21  * Note about the per-device constraint data struct allocation:
  22  * . The per-device constraints data struct ptr is tored into the device
  23  *    dev_pm_info.
  24  * . To minimize the data usage by the per-device constraints, the data struct
  25  *   is only allocated at the first call to dev_pm_qos_add_request.
  26  * . The data is later free'd when the device is removed from the system.
  27  * . The constraints_state variable from dev_pm_info tracks the data struct
  28  *    allocation state:
  29  *    DEV_PM_QOS_NO_DEVICE: No device present or device removed, no data
  30  *     allocated,
  31  *    DEV_PM_QOS_DEVICE_PRESENT: Device present, data not allocated and will be
  32  *     allocated at the first call to dev_pm_qos_add_request,
  33  *    DEV_PM_QOS_ALLOCATED: Device present, data allocated. The per-device
  34  *     PM QoS constraints framework is operational and constraints can be
  35  *     added, updated or removed using the dev_pm_qos_* API.
  36  *  . A global mutex protects the constraints users from the data being
  37  *     allocated and free'd.
  38  */
  39
  40 #include <linux/pm_qos.h>
  41 #include <linux/spinlock.h>
  42 #include <linux/slab.h>
  43 #include <linux/device.h>
  44 #include <linux/mutex.h>
  45
  46
  47 static DEFINE_MUTEX(dev_pm_qos_mtx);
  48
  49 /*
  50  * dev_pm_qos_constraints_allocate
  51  * @dev: device to allocate data for
  52  *
  53  * Called at the first call to add_request, for constraint data allocation
  54  * Must be called with the dev_pm_qos_mtx mutex held
  55  */
  56 static int dev_pm_qos_constraints_allocate(struct device *dev)
  57 {
  58         struct pm_qos_constraints *c;
  59         struct blocking_notifier_head *n;
  60
  61         c = kzalloc(sizeof(*c), GFP_KERNEL);
  62         if (!c)
  63                 return -ENOMEM;
  64
  65         n = kzalloc(sizeof(*n), GFP_KERNEL);
  66         if (!n) {
  67                 kfree(c);
  68                 return -ENOMEM;
  69         }
  70         BLOCKING_INIT_NOTIFIER_HEAD(n);
  71
  72         dev->power.constraints = c;
  73         plist_head_init(&dev->power.constraints->list);
  74         dev->power.constraints->target_value = PM_QOS_DEV_LAT_DEFAULT_VALUE;
  75         dev->power.constraints->default_value = PM_QOS_DEV_LAT_DEFAULT_VALUE;
  76         dev->power.constraints->type = PM_QOS_MIN;
  77         dev->power.constraints->notifiers = n;
  78         dev->power.constraints_state = DEV_PM_QOS_ALLOCATED;
  79
  80         return 0;
  81 }
  82
  83 /**
  84  * dev_pm_qos_constraints_init
  85  * @dev: target device
  86  *
  87  * Called from the device PM subsystem at device insertion
  88  */
  89 void dev_pm_qos_constraints_init(struct device *dev)
  90 {
  91         mutex_lock(&dev_pm_qos_mtx);
  92         dev->power.constraints_state = DEV_PM_QOS_DEVICE_PRESENT;
  93         mutex_unlock(&dev_pm_qos_mtx);
  94 }
  95
  96 /**
  97  * dev_pm_qos_constraints_destroy
  98  * @dev: target device
  99  *
 100  * Called from the device PM subsystem at device removal
 101  */
 102 void dev_pm_qos_constraints_destroy(struct device *dev)
 103 {
 104         struct dev_pm_qos_request *req, *tmp;
 105
 106         mutex_lock(&dev_pm_qos_mtx);
 107
 108         if (dev->power.constraints_state == DEV_PM_QOS_ALLOCATED) {
 109                 /* Flush the constraints list for the device */
 110                 plist_for_each_entry_safe(req, tmp,
 111                                           &dev->power.constraints->list,
 112                                           node) {
 113                         /*
 114                          * Update constraints list and call the per-device
 115                          * callbacks if needed
 116                          */
 117                         pm_qos_update_target(req->dev->power.constraints,
 118                                            &req->node, PM_QOS_REMOVE_REQ,
 119                                            PM_QOS_DEFAULT_VALUE);
 120                         memset(req, 0, sizeof(*req));
 121                 }
 122
 123                 kfree(dev->power.constraints->notifiers);
 124                 kfree(dev->power.constraints);
 125                 dev->power.constraints = NULL;
 126         }
 127         dev->power.constraints_state = DEV_PM_QOS_NO_DEVICE;
 128
 129         mutex_unlock(&dev_pm_qos_mtx);
 130 }
 131
 132 /**
 133  * dev_pm_qos_add_request - inserts new qos request into the list
 134  * @dev: target device for the constraint
 135  * @req: pointer to a preallocated handle
 136  * @value: defines the qos request
 137  *
 138  * This function inserts a new entry in the device constraints list of
 139  * requested qos performance characteristics. It recomputes the aggregate
 140  * QoS expectations of parameters and initializes the dev_pm_qos_request
 141  * handle.  Caller needs to save this handle for later use in updates and
 142  * removal.
 143  *
 144  * Returns 1 if the aggregated constraint value has changed,
 145  * 0 if the aggregated constraint value has not changed,
 146  * -EINVAL in case of wrong parameters, -ENODEV if the device has been
 147  * removed from the system
 148  */
 149 int dev_pm_qos_add_request(struct device *dev, struct dev_pm_qos_request *req,
 150                             s32 value)
 151 {
 152         int ret = 0;
 153
 154         if (!dev || !req) /*guard against callers passing in null */
 155                 return -EINVAL;
 156
 157         if (dev_pm_qos_request_active(req)) {
 158                 WARN(1, KERN_ERR "dev_pm_qos_add_request() called for already "
 159                         "added request\n");
 160                 return -EINVAL;
 161         }
 162
 163         mutex_lock(&dev_pm_qos_mtx);
 164         req->dev = dev;
 165
 166         /* Return if the device has been removed */
 167         if (req->dev->power.constraints_state == DEV_PM_QOS_NO_DEVICE) {
 168                 ret = -ENODEV;
 169                 goto out;
 170         }
 171
 172         /*
 173          * Allocate the constraints data on the first call to add_request,
 174          * i.e. only if the data is not already allocated and if the device has
 175          * not been removed
 176          */
 177         if (dev->power.constraints_state == DEV_PM_QOS_DEVICE_PRESENT)
 178                 ret = dev_pm_qos_constraints_allocate(dev);
 179
 180         if (!ret)
 181                 ret = pm_qos_update_target(dev->power.constraints, &req->node,
 182                                            PM_QOS_ADD_REQ, value);
 183
 184 out:
 185         mutex_unlock(&dev_pm_qos_mtx);
 186         return ret;
 187 }
 188 EXPORT_SYMBOL_GPL(dev_pm_qos_add_request);
 189
 190 /**
 191  * dev_pm_qos_update_request - modifies an existing qos request
 192  * @req : handle to list element holding a dev_pm_qos request to use
 193  * @new_value: defines the qos request
 194  *
 195  * Updates an existing dev PM qos request along with updating the
 196  * target value.
 197  *
 198  * Attempts are made to make this code callable on hot code paths.
 199  *
 200  * Returns 1 if the aggregated constraint value has changed,
 201  * 0 if the aggregated constraint value has not changed,
 202  * -EINVAL in case of wrong parameters, -ENODEV if the device has been
 203  * removed from the system
 204  */
 205 int dev_pm_qos_update_request(struct dev_pm_qos_request *req,
 206                               s32 new_value)
 207 {
 208         int ret = 0;
 209
 210         if (!req) /*guard against callers passing in null */
 211                 return -EINVAL;
 212
 213         if (!dev_pm_qos_request_active(req)) {
 214                 WARN(1, KERN_ERR "dev_pm_qos_update_request() called for "
 215                         "unknown object\n");
 216                 return -EINVAL;
 217         }
 218
 219         mutex_lock(&dev_pm_qos_mtx);
 220
 221         if (req->dev->power.constraints_state == DEV_PM_QOS_ALLOCATED) {
 222                 if (new_value != req->node.prio)
 223                         ret = pm_qos_update_target(req->dev->power.constraints,
 224                                                    &req->node,
 225                                                    PM_QOS_UPDATE_REQ,
 226                                                    new_value);
 227         } else {
 228                 /* Return if the device has been removed */
 229                 ret = -ENODEV;
 230         }
 231
 232         mutex_unlock(&dev_pm_qos_mtx);
 233         return ret;
 234 }
 235 EXPORT_SYMBOL_GPL(dev_pm_qos_update_request);
 236
 237 /**
 238  * dev_pm_qos_remove_request - modifies an existing qos request
 239  * @req: handle to request list element
 240  *
 241  * Will remove pm qos request from the list of constraints and
 242  * recompute the current target value. Call this on slow code paths.
 243  *
 244  * Returns 1 if the aggregated constraint value has changed,
 245  * 0 if the aggregated constraint value has not changed,
 246  * -EINVAL in case of wrong parameters, -ENODEV if the device has been
 247  * removed from the system
 248  */
 249 int dev_pm_qos_remove_request(struct dev_pm_qos_request *req)
 250 {
 251         int ret = 0;
 252
 253         if (!req) /*guard against callers passing in null */
 254                 return -EINVAL;
 255
 256         if (!dev_pm_qos_request_active(req)) {
 257                 WARN(1, KERN_ERR "dev_pm_qos_remove_request() called for "
 258                         "unknown object\n");
 259                 return -EINVAL;
 260         }
 261
 262         mutex_lock(&dev_pm_qos_mtx);
 263
 264         if (req->dev->power.constraints_state == DEV_PM_QOS_ALLOCATED) {
 265                 ret = pm_qos_update_target(req->dev->power.constraints,
 266                                            &req->node, PM_QOS_REMOVE_REQ,
 267                                            PM_QOS_DEFAULT_VALUE);
 268                 memset(req, 0, sizeof(*req));
 269         } else {
 270                 /* Return if the device has been removed */
 271                 ret = -ENODEV;
 272         }
 273
 274         mutex_unlock(&dev_pm_qos_mtx);
 275         return ret;
 276 }
 277 EXPORT_SYMBOL_GPL(dev_pm_qos_remove_request);
 278
 279 /**
 280  * dev_pm_qos_add_notifier - sets notification entry for changes to target value
 281  * of per-device PM QoS constraints
 282  *
 283  * @dev: target device for the constraint
 284  * @notifier: notifier block managed by caller.
 285  *
 286  * Will register the notifier into a notification chain that gets called
 287  * upon changes to the target value for the device.
 288  */
 289 int dev_pm_qos_add_notifier(struct device *dev, struct notifier_block *notifier)
 290 {
 291         int retval = 0;
 292
 293         mutex_lock(&dev_pm_qos_mtx);
 294
 295         /* Silently return if the device has been removed */
 296         if (dev->power.constraints_state != DEV_PM_QOS_ALLOCATED)
 297                 goto out;
 298
 299         retval = blocking_notifier_chain_register(
 300                         dev->power.constraints->notifiers,
 301                         notifier);
 302
 303 out:
 304         mutex_unlock(&dev_pm_qos_mtx);
 305         return retval;
 306 }
 307 EXPORT_SYMBOL_GPL(dev_pm_qos_add_notifier);
 308
 309 /**
 310  * dev_pm_qos_remove_notifier - deletes notification for changes to target value
 311  * of per-device PM QoS constraints
 312  *
 313  * @dev: target device for the constraint
 314  * @notifier: notifier block to be removed.
 315  *
 316  * Will remove the notifier from the notification chain that gets called
 317  * upon changes to the target value.
 318  */
 319 int dev_pm_qos_remove_notifier(struct device *dev,
 320                                struct notifier_block *notifier)
 321 {
 322         int retval = 0;
 323
 324         mutex_lock(&dev_pm_qos_mtx);
 325
 326         /* Silently return if the device has been removed */
 327         if (dev->power.constraints_state != DEV_PM_QOS_ALLOCATED)
 328                 goto out;
 329
 330         retval = blocking_notifier_chain_unregister(
 331                         dev->power.constraints->notifiers,
 332                         notifier);
 333
 334 out:
 335         mutex_unlock(&dev_pm_qos_mtx);
 336         return retval;
 337 }
 338 EXPORT_SYMBOL_GPL(dev_pm_qos_remove_notifier);