drivers/dma/dmaengine.c

   1 /*
   2  * Copyright(c) 2004 - 2006 Intel Corporation. All rights reserved.
   3  *
   4  * This program is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License as published by the Free
   6  * Software Foundation; either version 2 of the License, or (at your option)
   7  * any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  12  * more details.
  13  *
  14  * You should have received a copy of the GNU General Public License along with
  15  * this program; if not, write to the Free Software Foundation, Inc., 59
  16  * Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  17  *
  18  * The full GNU General Public License is included in this distribution in the
  19  * file called COPYING.
  20  */
  21
  22 /*
  23  * This code implements the DMA subsystem. It provides a HW-neutral interface
  24  * for other kernel code to use asynchronous memory copy capabilities,
  25  * if present, and allows different HW DMA drivers to register as providing
  26  * this capability.
  27  *
  28  * Due to the fact we are accelerating what is already a relatively fast
  29  * operation, the code goes to great lengths to avoid additional overhead,
  30  * such as locking.
  31  *
  32  * LOCKING:
  33  *
  34  * The subsystem keeps two global lists, dma_device_list and dma_client_list.
  35  * Both of these are protected by a mutex, dma_list_mutex.
  36  *
  37  * Each device has a channels list, which runs unlocked but is never modified
  38  * once the device is registered, it's just setup by the driver.
  39  *
  40  * Each client has a channels list, it's only modified under the client->lock
  41  * and in an RCU callback, so it's safe to read under rcu_read_lock().
  42  *
  43  * Each device has a kref, which is initialized to 1 when the device is
  44  * registered. A kref_put is done for each class_device registered.  When the
  45  * class_device is released, the coresponding kref_put is done in the release
  46  * method. Every time one of the device's channels is allocated to a client,
  47  * a kref_get occurs.  When the channel is freed, the coresponding kref_put
  48  * happens. The device's release function does a completion, so
  49  * unregister_device does a remove event, class_device_unregister, a kref_put
  50  * for the first reference, then waits on the completion for all other
  51  * references to finish.
  52  *
  53  * Each channel has an open-coded implementation of Rusty Russell's "bigref,"
  54  * with a kref and a per_cpu local_t.  A single reference is set when on an
  55  * ADDED event, and removed with a REMOVE event.  Net DMA client takes an
  56  * extra reference per outstanding transaction.  The relase function does a
  57  * kref_put on the device. -ChrisL
  58  */
  59
  60 #include <linux/init.h>
  61 #include <linux/module.h>
  62 #include <linux/device.h>
  63 #include <linux/dmaengine.h>
  64 #include <linux/hardirq.h>
  65 #include <linux/spinlock.h>
  66 #include <linux/percpu.h>
  67 #include <linux/rcupdate.h>
  68 #include <linux/mutex.h>
  69
  70 static DEFINE_MUTEX(dma_list_mutex);
  71 static LIST_HEAD(dma_device_list);
  72 static LIST_HEAD(dma_client_list);
  73
  74 /* --- sysfs implementation --- */
  75
  76 static ssize_t show_memcpy_count(struct class_device *cd, char *buf)
  77 {
  78         struct dma_chan *chan = container_of(cd, struct dma_chan, class_dev);
  79         unsigned long count = 0;
  80         int i;
  81
  82         for_each_possible_cpu(i)
  83                 count += per_cpu_ptr(chan->local, i)->memcpy_count;
  84
  85         return sprintf(buf, "%lu\n", count);
  86 }
  87
  88 static ssize_t show_bytes_transferred(struct class_device *cd, char *buf)
  89 {
  90         struct dma_chan *chan = container_of(cd, struct dma_chan, class_dev);
  91         unsigned long count = 0;
  92         int i;
  93
  94         for_each_possible_cpu(i)
  95                 count += per_cpu_ptr(chan->local, i)->bytes_transferred;
  96
  97         return sprintf(buf, "%lu\n", count);
  98 }
  99
 100 static ssize_t show_in_use(struct class_device *cd, char *buf)
 101 {
 102         struct dma_chan *chan = container_of(cd, struct dma_chan, class_dev);
 103
 104         return sprintf(buf, "%d\n", (chan->client ? 1 : 0));
 105 }
 106
 107 static struct class_device_attribute dma_class_attrs[] = {
 108         __ATTR(memcpy_count, S_IRUGO, show_memcpy_count, NULL),
 109         __ATTR(bytes_transferred, S_IRUGO, show_bytes_transferred, NULL),
 110         __ATTR(in_use, S_IRUGO, show_in_use, NULL),
 111         __ATTR_NULL
 112 };
 113
 114 static void dma_async_device_cleanup(struct kref *kref);
 115
 116 static void dma_class_dev_release(struct class_device *cd)
 117 {
 118         struct dma_chan *chan = container_of(cd, struct dma_chan, class_dev);
 119         kref_put(&chan->device->refcount, dma_async_device_cleanup);
 120 }
 121
 122 static struct class dma_devclass = {
 123         .name            = "dma",
 124         .class_dev_attrs = dma_class_attrs,
 125         .release = dma_class_dev_release,
 126 };
 127
 128 /* --- client and device registration --- */
 129
 130 /**
 131  * dma_client_chan_alloc - try to allocate a channel to a client
 132  * @client: &dma_client
 133  *
 134  * Called with dma_list_mutex held.
 135  */
 136 static struct dma_chan *dma_client_chan_alloc(struct dma_client *client)
 137 {
 138         struct dma_device *device;
 139         struct dma_chan *chan;
 140         unsigned long flags;
 141         int desc;       /* allocated descriptor count */
 142
 143         /* Find a channel, any DMA engine will do */
 144         list_for_each_entry(device, &dma_device_list, global_node) {
 145                 list_for_each_entry(chan, &device->channels, device_node) {
 146                         if (chan->client)
 147                                 continue;
 148
 149                         desc = chan->device->device_alloc_chan_resources(chan);
 150                         if (desc >= 0) {
 151                                 kref_get(&device->refcount);
 152                                 kref_init(&chan->refcount);
 153                                 chan->slow_ref = 0;
 154                                 INIT_RCU_HEAD(&chan->rcu);
 155                                 chan->client = client;
 156                                 spin_lock_irqsave(&client->lock, flags);
 157                                 list_add_tail_rcu(&chan->client_node,
 158                                                   &client->channels);
 159                                 spin_unlock_irqrestore(&client->lock, flags);
 160                                 return chan;
 161                         }
 162                 }
 163         }
 164
 165         return NULL;
 166 }
 167
 168 /**
 169  * dma_chan_cleanup - release a DMA channel's resources
 170  * @kref: kernel reference structure that contains the DMA channel device
 171  */
 172 void dma_chan_cleanup(struct kref *kref)
 173 {
 174         struct dma_chan *chan = container_of(kref, struct dma_chan, refcount);
 175         chan->device->device_free_chan_resources(chan);
 176         chan->client = NULL;
 177         kref_put(&chan->device->refcount, dma_async_device_cleanup);
 178 }
 179 EXPORT_SYMBOL(dma_chan_cleanup);
 180
 181 static void dma_chan_free_rcu(struct rcu_head *rcu)
 182 {
 183         struct dma_chan *chan = container_of(rcu, struct dma_chan, rcu);
 184         int bias = 0x7FFFFFFF;
 185         int i;
 186         for_each_possible_cpu(i)
 187                 bias -= local_read(&per_cpu_ptr(chan->local, i)->refcount);
 188         atomic_sub(bias, &chan->refcount.refcount);
 189         kref_put(&chan->refcount, dma_chan_cleanup);
 190 }
 191
 192 static void dma_client_chan_free(struct dma_chan *chan)
 193 {
 194         atomic_add(0x7FFFFFFF, &chan->refcount.refcount);
 195         chan->slow_ref = 1;
 196         call_rcu(&chan->rcu, dma_chan_free_rcu);
 197 }
 198
 199 /**
 200  * dma_chans_rebalance - reallocate channels to clients
 201  *
 202  * When the number of DMA channel in the system changes,
 203  * channels need to be rebalanced among clients.
 204  */
 205 static void dma_chans_rebalance(void)
 206 {
 207         struct dma_client *client;
 208         struct dma_chan *chan;
 209         unsigned long flags;
 210
 211         mutex_lock(&dma_list_mutex);
 212
 213         list_for_each_entry(client, &dma_client_list, global_node) {
 214                 while (client->chans_desired > client->chan_count) {
 215                         chan = dma_client_chan_alloc(client);
 216                         if (!chan)
 217                                 break;
 218                         client->chan_count++;
 219                         client->event_callback(client,
 220                                                chan,
 221                                                DMA_RESOURCE_ADDED);
 222                 }
 223                 while (client->chans_desired < client->chan_count) {
 224                         spin_lock_irqsave(&client->lock, flags);
 225                         chan = list_entry(client->channels.next,
 226                                           struct dma_chan,
 227                                           client_node);
 228                         list_del_rcu(&chan->client_node);
 229                         spin_unlock_irqrestore(&client->lock, flags);
 230                         client->chan_count--;
 231                         client->event_callback(client,
 232                                                chan,
 233                                                DMA_RESOURCE_REMOVED);
 234                         dma_client_chan_free(chan);
 235                 }
 236         }
 237
 238         mutex_unlock(&dma_list_mutex);
 239 }
 240
 241 /**
 242  * dma_async_client_register - allocate and register a &dma_client
 243  * @event_callback: callback for notification of channel addition/removal
 244  */
 245 struct dma_client *dma_async_client_register(dma_event_callback event_callback)
 246 {
 247         struct dma_client *client;
 248
 249         client = kzalloc(sizeof(*client), GFP_KERNEL);
 250         if (!client)
 251                 return NULL;
 252
 253         INIT_LIST_HEAD(&client->channels);
 254         spin_lock_init(&client->lock);
 255         client->chans_desired = 0;
 256         client->chan_count = 0;
 257         client->event_callback = event_callback;
 258
 259         mutex_lock(&dma_list_mutex);
 260         list_add_tail(&client->global_node, &dma_client_list);
 261         mutex_unlock(&dma_list_mutex);
 262
 263         return client;
 264 }
 265 EXPORT_SYMBOL(dma_async_client_register);
 266
 267 /**
 268  * dma_async_client_unregister - unregister a client and free the &dma_client
 269  * @client: &dma_client to free
 270  *
 271  * Force frees any allocated DMA channels, frees the &dma_client memory
 272  */
 273 void dma_async_client_unregister(struct dma_client *client)
 274 {
 275         struct dma_chan *chan;
 276
 277         if (!client)
 278                 return;
 279
 280         rcu_read_lock();
 281         list_for_each_entry_rcu(chan, &client->channels, client_node)
 282                 dma_client_chan_free(chan);
 283         rcu_read_unlock();
 284
 285         mutex_lock(&dma_list_mutex);
 286         list_del(&client->global_node);
 287         mutex_unlock(&dma_list_mutex);
 288
 289         kfree(client);
 290         dma_chans_rebalance();
 291 }
 292 EXPORT_SYMBOL(dma_async_client_unregister);
 293
 294 /**
 295  * dma_async_client_chan_request - request DMA channels
 296  * @client: &dma_client
 297  * @number: count of DMA channels requested
 298  *
 299  * Clients call dma_async_client_chan_request() to specify how many
 300  * DMA channels they need, 0 to free all currently allocated.
 301  * The resulting allocations/frees are indicated to the client via the
 302  * event callback.
 303  */
 304 void dma_async_client_chan_request(struct dma_client *client,
 305                         unsigned int number)
 306 {
 307         client->chans_desired = number;
 308         dma_chans_rebalance();
 309 }
 310 EXPORT_SYMBOL(dma_async_client_chan_request);
 311
 312 /**
 313  * dma_async_device_register - registers DMA devices found
 314  * @device: &dma_device
 315  */
 316 int dma_async_device_register(struct dma_device *device)
 317 {
 318         static int id;
 319         int chancnt = 0;
 320         struct dma_chan* chan;
 321
 322         if (!device)
 323                 return -ENODEV;
 324
 325         init_completion(&device->done);
 326         kref_init(&device->refcount);
 327         device->dev_id = id++;
 328
 329         /* represent channels in sysfs. Probably want devs too */
 330         list_for_each_entry(chan, &device->channels, device_node) {
 331                 chan->local = alloc_percpu(typeof(*chan->local));
 332                 if (chan->local == NULL)
 333                         continue;
 334
 335                 chan->chan_id = chancnt++;
 336                 chan->class_dev.class = &dma_devclass;
 337                 chan->class_dev.dev = NULL;
 338                 snprintf(chan->class_dev.class_id, BUS_ID_SIZE, "dma%dchan%d",
 339                          device->dev_id, chan->chan_id);
 340
 341                 kref_get(&device->refcount);
 342                 class_device_register(&chan->class_dev);
 343         }
 344
 345         mutex_lock(&dma_list_mutex);
 346         list_add_tail(&device->global_node, &dma_device_list);
 347         mutex_unlock(&dma_list_mutex);
 348
 349         dma_chans_rebalance();
 350
 351         return 0;
 352 }
 353 EXPORT_SYMBOL(dma_async_device_register);
 354
 355 /**
 356  * dma_async_device_cleanup - function called when all references are released
 357  * @kref: kernel reference object
 358  */
 359 static void dma_async_device_cleanup(struct kref *kref)
 360 {
 361         struct dma_device *device;
 362
 363         device = container_of(kref, struct dma_device, refcount);
 364         complete(&device->done);
 365 }
 366
 367 /**
 368  * dma_async_device_unregister - unregisters DMA devices
 369  * @device: &dma_device
 370  */
 371 void dma_async_device_unregister(struct dma_device *device)
 372 {
 373         struct dma_chan *chan;
 374         unsigned long flags;
 375
 376         mutex_lock(&dma_list_mutex);
 377         list_del(&device->global_node);
 378         mutex_unlock(&dma_list_mutex);
 379
 380         list_for_each_entry(chan, &device->channels, device_node) {
 381                 if (chan->client) {
 382                         spin_lock_irqsave(&chan->client->lock, flags);
 383                         list_del(&chan->client_node);
 384                         chan->client->chan_count--;
 385                         spin_unlock_irqrestore(&chan->client->lock, flags);
 386                         chan->client->event_callback(chan->client,
 387                                                      chan,
 388                                                      DMA_RESOURCE_REMOVED);
 389                         dma_client_chan_free(chan);
 390                 }
 391                 class_device_unregister(&chan->class_dev);
 392         }
 393         dma_chans_rebalance();
 394
 395         kref_put(&device->refcount, dma_async_device_cleanup);
 396         wait_for_completion(&device->done);
 397 }
 398 EXPORT_SYMBOL(dma_async_device_unregister);
 399
 400 static int __init dma_bus_init(void)
 401 {
 402         mutex_init(&dma_list_mutex);
 403         return class_register(&dma_devclass);
 404 }
 405 subsys_initcall(dma_bus_init);
 406