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Tejun Heo9ac78492007-01-20 16:00:26 +09001Devres - Managed Device Resource
2================================
3
4Tejun Heo <teheo@suse.de>
5
6First draft 10 January 2007
7
8
91. Intro : Huh? Devres?
102. Devres : Devres in a nutshell
113. Devres Group : Group devres'es and release them together
124. Details : Life time rules, calling context, ...
135. Overhead : How much do we have to pay for this?
146. List of managed interfaces : Currently implemented managed interfaces
15
16
17 1. Intro
18 --------
19
20devres came up while trying to convert libata to use iomap. Each
21iomapped address should be kept and unmapped on driver detach. For
22example, a plain SFF ATA controller (that is, good old PCI IDE) in
23native mode makes use of 5 PCI BARs and all of them should be
24maintained.
25
26As with many other device drivers, libata low level drivers have
27sufficient bugs in ->remove and ->probe failure path. Well, yes,
28that's probably because libata low level driver developers are lazy
29bunch, but aren't all low level driver developers? After spending a
30day fiddling with braindamaged hardware with no document or
31braindamaged document, if it's finally working, well, it's working.
32
33For one reason or another, low level drivers don't receive as much
34attention or testing as core code, and bugs on driver detach or
Matt LaPlante01dd2fb2007-10-20 01:34:40 +020035initialization failure don't happen often enough to be noticeable.
Tejun Heo9ac78492007-01-20 16:00:26 +090036Init failure path is worse because it's much less travelled while
37needs to handle multiple entry points.
38
39So, many low level drivers end up leaking resources on driver detach
40and having half broken failure path implementation in ->probe() which
41would leak resources or even cause oops when failure occurs. iomap
42adds more to this mix. So do msi and msix.
43
44
45 2. Devres
46 ---------
47
48devres is basically linked list of arbitrarily sized memory areas
49associated with a struct device. Each devres entry is associated with
50a release function. A devres can be released in several ways. No
51matter what, all devres entries are released on driver detach. On
52release, the associated release function is invoked and then the
53devres entry is freed.
54
55Managed interface is created for resources commonly used by device
56drivers using devres. For example, coherent DMA memory is acquired
57using dma_alloc_coherent(). The managed version is called
58dmam_alloc_coherent(). It is identical to dma_alloc_coherent() except
59for the DMA memory allocated using it is managed and will be
60automatically released on driver detach. Implementation looks like
61the following.
62
63 struct dma_devres {
64 size_t size;
65 void *vaddr;
66 dma_addr_t dma_handle;
67 };
68
69 static void dmam_coherent_release(struct device *dev, void *res)
70 {
71 struct dma_devres *this = res;
72
73 dma_free_coherent(dev, this->size, this->vaddr, this->dma_handle);
74 }
75
76 dmam_alloc_coherent(dev, size, dma_handle, gfp)
77 {
78 struct dma_devres *dr;
79 void *vaddr;
80
81 dr = devres_alloc(dmam_coherent_release, sizeof(*dr), gfp);
82 ...
83
84 /* alloc DMA memory as usual */
85 vaddr = dma_alloc_coherent(...);
86 ...
87
88 /* record size, vaddr, dma_handle in dr */
89 dr->vaddr = vaddr;
90 ...
91
92 devres_add(dev, dr);
93
94 return vaddr;
95 }
96
97If a driver uses dmam_alloc_coherent(), the area is guaranteed to be
98freed whether initialization fails half-way or the device gets
99detached. If most resources are acquired using managed interface, a
100driver can have much simpler init and exit code. Init path basically
101looks like the following.
102
103 my_init_one()
104 {
105 struct mydev *d;
106
107 d = devm_kzalloc(dev, sizeof(*d), GFP_KERNEL);
108 if (!d)
109 return -ENOMEM;
110
111 d->ring = dmam_alloc_coherent(...);
112 if (!d->ring)
113 return -ENOMEM;
114
115 if (check something)
116 return -EINVAL;
117 ...
118
119 return register_to_upper_layer(d);
120 }
121
122And exit path,
123
124 my_remove_one()
125 {
126 unregister_from_upper_layer(d);
127 shutdown_my_hardware();
128 }
129
130As shown above, low level drivers can be simplified a lot by using
131devres. Complexity is shifted from less maintained low level drivers
132to better maintained higher layer. Also, as init failure path is
133shared with exit path, both can get more testing.
134
135
136 3. Devres group
137 ---------------
138
139Devres entries can be grouped using devres group. When a group is
140released, all contained normal devres entries and properly nested
141groups are released. One usage is to rollback series of acquired
142resources on failure. For example,
143
144 if (!devres_open_group(dev, NULL, GFP_KERNEL))
145 return -ENOMEM;
146
147 acquire A;
148 if (failed)
149 goto err;
150
151 acquire B;
152 if (failed)
153 goto err;
154 ...
155
156 devres_remove_group(dev, NULL);
157 return 0;
158
159 err:
160 devres_release_group(dev, NULL);
161 return err_code;
162
Matt LaPlante01dd2fb2007-10-20 01:34:40 +0200163As resource acquisition failure usually means probe failure, constructs
Tejun Heo9ac78492007-01-20 16:00:26 +0900164like above are usually useful in midlayer driver (e.g. libata core
165layer) where interface function shouldn't have side effect on failure.
166For LLDs, just returning error code suffices in most cases.
167
168Each group is identified by void *id. It can either be explicitly
169specified by @id argument to devres_open_group() or automatically
170created by passing NULL as @id as in the above example. In both
171cases, devres_open_group() returns the group's id. The returned id
172can be passed to other devres functions to select the target group.
173If NULL is given to those functions, the latest open group is
174selected.
175
176For example, you can do something like the following.
177
178 int my_midlayer_create_something()
179 {
180 if (!devres_open_group(dev, my_midlayer_create_something, GFP_KERNEL))
181 return -ENOMEM;
182
183 ...
184
Rolf Eike Beer3265b542007-05-01 11:00:19 +0200185 devres_close_group(dev, my_midlayer_create_something);
Tejun Heo9ac78492007-01-20 16:00:26 +0900186 return 0;
187 }
188
189 void my_midlayer_destroy_something()
190 {
Matt LaPlante19f59462009-04-27 15:06:31 +0200191 devres_release_group(dev, my_midlayer_create_something);
Tejun Heo9ac78492007-01-20 16:00:26 +0900192 }
193
194
195 4. Details
196 ----------
197
198Lifetime of a devres entry begins on devres allocation and finishes
199when it is released or destroyed (removed and freed) - no reference
200counting.
201
202devres core guarantees atomicity to all basic devres operations and
203has support for single-instance devres types (atomic
204lookup-and-add-if-not-found). Other than that, synchronizing
205concurrent accesses to allocated devres data is caller's
206responsibility. This is usually non-issue because bus ops and
207resource allocations already do the job.
208
209For an example of single-instance devres type, read pcim_iomap_table()
Brandon Philips2c19c492007-07-17 22:09:34 -0700210in lib/devres.c.
Tejun Heo9ac78492007-01-20 16:00:26 +0900211
212All devres interface functions can be called without context if the
213right gfp mask is given.
214
215
216 5. Overhead
217 -----------
218
219Each devres bookkeeping info is allocated together with requested data
220area. With debug option turned off, bookkeeping info occupies 16
221bytes on 32bit machines and 24 bytes on 64bit (three pointers rounded
222up to ull alignment). If singly linked list is used, it can be
223reduced to two pointers (8 bytes on 32bit, 16 bytes on 64bit).
224
225Each devres group occupies 8 pointers. It can be reduced to 6 if
226singly linked list is used.
227
228Memory space overhead on ahci controller with two ports is between 300
229and 400 bytes on 32bit machine after naive conversion (we can
230certainly invest a bit more effort into libata core layer).
231
232
233 6. List of managed interfaces
234 -----------------------------
235
Geert Uytterhoevend8e1e012014-07-10 10:10:23 +0200236CLOCK
237 devm_clk_get()
238 devm_clk_put()
Stephen Boyd41438042016-02-05 17:02:52 -0800239 devm_clk_hw_register()
Geert Uytterhoevend8e1e012014-07-10 10:10:23 +0200240
241DMA
242 dmam_alloc_coherent()
243 dmam_alloc_noncoherent()
244 dmam_declare_coherent_memory()
245 dmam_free_coherent()
246 dmam_free_noncoherent()
247 dmam_pool_create()
248 dmam_pool_destroy()
249
250GPIO
251 devm_gpiod_get()
252 devm_gpiod_get_index()
253 devm_gpiod_get_index_optional()
254 devm_gpiod_get_optional()
255 devm_gpiod_put()
Laxman Dewangan38115ea2016-02-22 15:00:08 +0530256 devm_gpiochip_add_data()
257 devm_gpiochip_remove()
Laxman Dewangan77ae5822016-02-22 15:04:08 +0530258 devm_gpio_request()
259 devm_gpio_request_one()
260 devm_gpio_free()
Wolfram Sang543f43c2012-01-15 13:31:46 +0100261
Oleksandr Kravchenko224b9952013-07-23 09:39:00 +0100262IIO
263 devm_iio_device_alloc()
264 devm_iio_device_free()
Sachin Kamat8caa07c2013-10-29 11:39:00 +0000265 devm_iio_device_register()
266 devm_iio_device_unregister()
Karol Wrona780103f2014-12-19 18:39:25 +0100267 devm_iio_kfifo_allocate()
268 devm_iio_kfifo_free()
Gregor Boirie70e48342016-09-02 20:47:55 +0200269 devm_iio_triggered_buffer_setup()
270 devm_iio_triggered_buffer_cleanup()
Geert Uytterhoevend8e1e012014-07-10 10:10:23 +0200271 devm_iio_trigger_alloc()
272 devm_iio_trigger_free()
Gregor Boirie90833252016-09-02 20:47:54 +0200273 devm_iio_trigger_register()
274 devm_iio_trigger_unregister()
Laxman Dewangane21a2942016-04-06 16:01:08 +0530275 devm_iio_channel_get()
276 devm_iio_channel_release()
277 devm_iio_channel_get_all()
278 devm_iio_channel_release_all()
Oleksandr Kravchenko224b9952013-07-23 09:39:00 +0100279
Alexander Kurz2ea2dc82016-04-21 19:02:04 +0200280INPUT
281 devm_input_allocate_device()
282
Tejun Heo9ac78492007-01-20 16:00:26 +0900283IO region
Tejun Heo9ac78492007-01-20 16:00:26 +0900284 devm_release_mem_region()
Geert Uytterhoevend8e1e012014-07-10 10:10:23 +0200285 devm_release_region()
Thierry Reding8d388212014-08-01 14:15:10 +0200286 devm_release_resource()
Geert Uytterhoevend8e1e012014-07-10 10:10:23 +0200287 devm_request_mem_region()
288 devm_request_region()
Thierry Reding8d388212014-08-01 14:15:10 +0200289 devm_request_resource()
Tejun Heo9ac78492007-01-20 16:00:26 +0900290
291IOMAP
292 devm_ioport_map()
293 devm_ioport_unmap()
294 devm_ioremap()
295 devm_ioremap_nocache()
Abhilash Kesavan34644522015-02-06 19:15:27 +0530296 devm_ioremap_wc()
Thierry Reding75096572013-01-21 11:08:54 +0100297 devm_ioremap_resource() : checks resource, requests memory region, ioremaps
Geert Uytterhoevend8e1e012014-07-10 10:10:23 +0200298 devm_iounmap()
Tejun Heo9ac78492007-01-20 16:00:26 +0900299 pcim_iomap()
Tejun Heo9ac78492007-01-20 16:00:26 +0900300 pcim_iomap_regions() : do request_region() and iomap() on multiple BARs
Geert Uytterhoevend8e1e012014-07-10 10:10:23 +0200301 pcim_iomap_table() : array of mapped addresses indexed by BAR
302 pcim_iounmap()
Stephen Boyd070b9072012-01-16 19:39:58 -0800303
Geert Uytterhoevend8e1e012014-07-10 10:10:23 +0200304IRQ
305 devm_free_irq()
Tobias Klauserea051662014-08-14 10:05:03 +0200306 devm_request_any_context_irq()
Geert Uytterhoevend8e1e012014-07-10 10:10:23 +0200307 devm_request_irq()
Tobias Klauserea051662014-08-14 10:05:03 +0200308 devm_request_threaded_irq()
Bartosz Golaszewski3e55cfc2017-08-14 16:53:17 +0200309 devm_irq_sim_init()
Mark Browna8a97db2012-04-05 11:42:09 +0100310
Bjorn Anderssonca1bb4e2015-02-23 16:11:41 -0800311LED
312 devm_led_classdev_register()
313 devm_led_classdev_unregister()
314
Geert Uytterhoevend8e1e012014-07-10 10:10:23 +0200315MDIO
316 devm_mdiobus_alloc()
317 devm_mdiobus_alloc_size()
318 devm_mdiobus_free()
319
320MEM
321 devm_free_pages()
322 devm_get_free_pages()
Geert Uytterhoevenbef59c52014-08-20 15:26:35 +0200323 devm_kasprintf()
Geert Uytterhoevend8e1e012014-07-10 10:10:23 +0200324 devm_kcalloc()
325 devm_kfree()
326 devm_kmalloc()
327 devm_kmalloc_array()
328 devm_kmemdup()
Geert Uytterhoeven54270352014-08-20 15:26:34 +0200329 devm_kstrdup()
Geert Uytterhoevenbef59c52014-08-20 15:26:35 +0200330 devm_kvasprintf()
Geert Uytterhoevend8e1e012014-07-10 10:10:23 +0200331 devm_kzalloc()
332
Laxman Dewangan36982832016-04-08 00:12:56 +0530333MFD
334 devm_mfd_add_devices()
335
Geert Uytterhoevend8e1e012014-07-10 10:10:23 +0200336PCI
337 pcim_enable_device() : after success, all PCI ops become managed
338 pcim_pin_device() : keep PCI device enabled after release
339
340PHY
341 devm_usb_get_phy()
342 devm_usb_put_phy()
Linus Torvalds3d1482f2012-05-21 16:58:23 -0700343
Stephen Warren6d4ca1f2012-04-16 10:51:00 -0600344PINCTRL
345 devm_pinctrl_get()
346 devm_pinctrl_put()
Laxman Dewangan1f8dd722016-02-24 14:14:35 +0530347 devm_pinctrl_register()
348 devm_pinctrl_unregister()
Alexandre Courbot63543162012-08-01 19:20:58 +0900349
Bjorn Anderssonc1a96342016-08-03 22:04:05 -0700350POWER
351 devm_reboot_mode_register()
352 devm_reboot_mode_unregister()
353
Alexandre Courbot63543162012-08-01 19:20:58 +0900354PWM
355 devm_pwm_get()
356 devm_pwm_put()
Marko Katic2202d4e2012-12-13 19:14:54 +0100357
Geert Uytterhoevend8e1e012014-07-10 10:10:23 +0200358REGULATOR
359 devm_regulator_bulk_get()
360 devm_regulator_get()
361 devm_regulator_put()
362 devm_regulator_register()
Andy Shevchenko0244d842013-08-21 14:27:05 +0300363
Masahiro Yamada8d5b5d52016-05-01 19:36:57 +0900364RESET
365 devm_reset_control_get()
366 devm_reset_controller_register()
367
Andy Shevchenko0244d842013-08-21 14:27:05 +0300368SLAVE DMA ENGINE
369 devm_acpi_dma_controller_register()
Mark Brown666d5b42013-08-31 18:50:52 +0100370
371SPI
372 devm_spi_register_master()
Neil Armstrong83fbae52016-05-27 17:33:54 +0200373
374WATCHDOG
375 devm_watchdog_register_device()