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1================================
2Devres - Managed Device Resource
3================================
4
5Tejun Heo <[email protected]>
6
7First draft 10 January 2007
8
9.. contents
10
11 1. Intro : Huh? Devres?
12 2. Devres : Devres in a nutshell
13 3. Devres Group : Group devres'es and release them together
14 4. Details : Life time rules, calling context, ...
15 5. Overhead : How much do we have to pay for this?
16 6. List of managed interfaces: Currently implemented managed interfaces
17
18
191. Intro
20--------
21
22devres came up while trying to convert libata to use iomap. Each
23iomapped address should be kept and unmapped on driver detach. For
24example, a plain SFF ATA controller (that is, good old PCI IDE) in
25native mode makes use of 5 PCI BARs and all of them should be
26maintained.
27
28As with many other device drivers, libata low level drivers have
29sufficient bugs in ->remove and ->probe failure path. Well, yes,
30that's probably because libata low level driver developers are lazy
31bunch, but aren't all low level driver developers? After spending a
32day fiddling with braindamaged hardware with no document or
33braindamaged document, if it's finally working, well, it's working.
34
35For one reason or another, low level drivers don't receive as much
36attention or testing as core code, and bugs on driver detach or
37initialization failure don't happen often enough to be noticeable.
38Init failure path is worse because it's much less travelled while
39needs to handle multiple entry points.
40
41So, many low level drivers end up leaking resources on driver detach
42and having half broken failure path implementation in ->probe() which
43would leak resources or even cause oops when failure occurs. iomap
44adds more to this mix. So do msi and msix.
45
46
472. Devres
48---------
49
50devres is basically linked list of arbitrarily sized memory areas
51associated with a struct device. Each devres entry is associated with
52a release function. A devres can be released in several ways. No
53matter what, all devres entries are released on driver detach. On
54release, the associated release function is invoked and then the
55devres entry is freed.
56
57Managed interface is created for resources commonly used by device
58drivers using devres. For example, coherent DMA memory is acquired
59using dma_alloc_coherent(). The managed version is called
60dmam_alloc_coherent(). It is identical to dma_alloc_coherent() except
61for the DMA memory allocated using it is managed and will be
62automatically released on driver detach. Implementation looks like
63the following::
64
65 struct dma_devres {
66 size_t size;
67 void *vaddr;
68 dma_addr_t dma_handle;
69 };
70
71 static void dmam_coherent_release(struct device *dev, void *res)
72 {
73 struct dma_devres *this = res;
74
75 dma_free_coherent(dev, this->size, this->vaddr, this->dma_handle);
76 }
77
78 dmam_alloc_coherent(dev, size, dma_handle, gfp)
79 {
80 struct dma_devres *dr;
81 void *vaddr;
82
83 dr = devres_alloc(dmam_coherent_release, sizeof(*dr), gfp);
84 ...
85
86 /* alloc DMA memory as usual */
87 vaddr = dma_alloc_coherent(...);
88 ...
89
90 /* record size, vaddr, dma_handle in dr */
91 dr->vaddr = vaddr;
92 ...
93
94 devres_add(dev, dr);
95
96 return vaddr;
97 }
98
99If a driver uses dmam_alloc_coherent(), the area is guaranteed to be
100freed whether initialization fails half-way or the device gets
101detached. If most resources are acquired using managed interface, a
102driver can have much simpler init and exit code. Init path basically
103looks like the following::
104
105 my_init_one()
106 {
107 struct mydev *d;
108
109 d = devm_kzalloc(dev, sizeof(*d), GFP_KERNEL);
110 if (!d)
111 return -ENOMEM;
112
113 d->ring = dmam_alloc_coherent(...);
114 if (!d->ring)
115 return -ENOMEM;
116
117 if (check something)
118 return -EINVAL;
119 ...
120
121 return register_to_upper_layer(d);
122 }
123
124And exit path::
125
126 my_remove_one()
127 {
128 unregister_from_upper_layer(d);
129 shutdown_my_hardware();
130 }
131
132As shown above, low level drivers can be simplified a lot by using
133devres. Complexity is shifted from less maintained low level drivers
134to better maintained higher layer. Also, as init failure path is
135shared with exit path, both can get more testing.
136
137Note though that when converting current calls or assignments to
138managed devm_* versions it is up to you to check if internal operations
139like allocating memory, have failed. Managed resources pertains to the
140freeing of these resources *only* - all other checks needed are still
141on you. In some cases this may mean introducing checks that were not
142necessary before moving to the managed devm_* calls.
143
144
1453. Devres group
146---------------
147
148Devres entries can be grouped using devres group. When a group is
149released, all contained normal devres entries and properly nested
150groups are released. One usage is to rollback series of acquired
151resources on failure. For example::
152
153 if (!devres_open_group(dev, NULL, GFP_KERNEL))
154 return -ENOMEM;
155
156 acquire A;
157 if (failed)
158 goto err;
159
160 acquire B;
161 if (failed)
162 goto err;
163 ...
164
165 devres_remove_group(dev, NULL);
166 return 0;
167
168 err:
169 devres_release_group(dev, NULL);
170 return err_code;
171
172As resource acquisition failure usually means probe failure, constructs
173like above are usually useful in midlayer driver (e.g. libata core
174layer) where interface function shouldn't have side effect on failure.
175For LLDs, just returning error code suffices in most cases.
176
177Each group is identified by `void *id`. It can either be explicitly
178specified by @id argument to devres_open_group() or automatically
179created by passing NULL as @id as in the above example. In both
180cases, devres_open_group() returns the group's id. The returned id
181can be passed to other devres functions to select the target group.
182If NULL is given to those functions, the latest open group is
183selected.
184
185For example, you can do something like the following::
186
187 int my_midlayer_create_something()
188 {
189 if (!devres_open_group(dev, my_midlayer_create_something, GFP_KERNEL))
190 return -ENOMEM;
191
192 ...
193
194 devres_close_group(dev, my_midlayer_create_something);
195 return 0;
196 }
197
198 void my_midlayer_destroy_something()
199 {
200 devres_release_group(dev, my_midlayer_create_something);
201 }
202
203
2044. Details
205----------
206
207Lifetime of a devres entry begins on devres allocation and finishes
208when it is released or destroyed (removed and freed) - no reference
209counting.
210
211devres core guarantees atomicity to all basic devres operations and
212has support for single-instance devres types (atomic
213lookup-and-add-if-not-found). Other than that, synchronizing
214concurrent accesses to allocated devres data is caller's
215responsibility. This is usually non-issue because bus ops and
216resource allocations already do the job.
217
218For an example of single-instance devres type, read pcim_iomap_table()
219in lib/devres.c.
220
221All devres interface functions can be called without context if the
222right gfp mask is given.
223
224
2255. Overhead
226-----------
227
228Each devres bookkeeping info is allocated together with requested data
229area. With debug option turned off, bookkeeping info occupies 16
230bytes on 32bit machines and 24 bytes on 64bit (three pointers rounded
231up to ull alignment). If singly linked list is used, it can be
232reduced to two pointers (8 bytes on 32bit, 16 bytes on 64bit).
233
234Each devres group occupies 8 pointers. It can be reduced to 6 if
235singly linked list is used.
236
237Memory space overhead on ahci controller with two ports is between 300
238and 400 bytes on 32bit machine after naive conversion (we can
239certainly invest a bit more effort into libata core layer).
240
241
2426. List of managed interfaces
243-----------------------------
244
245CLOCK
246 devm_clk_get()
247 devm_clk_get_optional()
248 devm_clk_put()
249 devm_clk_bulk_get()
250 devm_clk_bulk_get_all()
251 devm_clk_bulk_get_enable()
252 devm_clk_bulk_get_optional()
253 devm_get_clk_from_child()
254 devm_clk_hw_register()
255 devm_of_clk_add_hw_provider()
256 devm_clk_hw_register_clkdev()
257
258DMA
259 dmaenginem_async_device_register()
260 dmam_alloc_coherent()
261 dmam_alloc_attrs()
262 dmam_free_coherent()
263 dmam_pool_create()
264 dmam_pool_destroy()
265
266DRM
267 devm_drm_dev_alloc()
268
269GPIO
270 devm_gpiod_get()
271 devm_gpiod_get_array()
272 devm_gpiod_get_array_optional()
273 devm_gpiod_get_index()
274 devm_gpiod_get_index_optional()
275 devm_gpiod_get_optional()
276 devm_gpiod_put()
277 devm_gpiod_unhinge()
278 devm_gpiochip_add_data()
279 devm_gpio_request_one()
280
281I2C
282 devm_i2c_add_adapter()
283 devm_i2c_new_dummy_device()
284
285IIO
286 devm_iio_device_alloc()
287 devm_iio_device_register()
288 devm_iio_dmaengine_buffer_setup()
289 devm_iio_kfifo_buffer_setup()
290 devm_iio_kfifo_buffer_setup_ext()
291 devm_iio_map_array_register()
292 devm_iio_triggered_buffer_setup()
293 devm_iio_triggered_buffer_setup_ext()
294 devm_iio_trigger_alloc()
295 devm_iio_trigger_register()
296 devm_iio_channel_get()
297 devm_iio_channel_get_all()
298 devm_iio_hw_consumer_alloc()
299 devm_fwnode_iio_channel_get_by_name()
300
301INPUT
302 devm_input_allocate_device()
303
304IO region
305 devm_release_mem_region()
306 devm_release_region()
307 devm_release_resource()
308 devm_request_mem_region()
309 devm_request_free_mem_region()
310 devm_request_region()
311 devm_request_resource()
312
313IOMAP
314 devm_ioport_map()
315 devm_ioport_unmap()
316 devm_ioremap()
317 devm_ioremap_uc()
318 devm_ioremap_wc()
319 devm_ioremap_resource() : checks resource, requests memory region, ioremaps
320 devm_ioremap_resource_wc()
321 devm_platform_ioremap_resource() : calls devm_ioremap_resource() for platform device
322 devm_platform_ioremap_resource_byname()
323 devm_platform_get_and_ioremap_resource()
324 devm_iounmap()
325
326 Note: For the PCI devices the specific pcim_*() functions may be used, see below.
327
328IRQ
329 devm_free_irq()
330 devm_request_any_context_irq()
331 devm_request_irq()
332 devm_request_threaded_irq()
333 devm_irq_alloc_descs()
334 devm_irq_alloc_desc()
335 devm_irq_alloc_desc_at()
336 devm_irq_alloc_desc_from()
337 devm_irq_alloc_descs_from()
338 devm_irq_alloc_generic_chip()
339 devm_irq_setup_generic_chip()
340 devm_irq_domain_create_sim()
341
342LED
343 devm_led_classdev_register()
344 devm_led_classdev_register_ext()
345 devm_led_classdev_unregister()
346 devm_led_trigger_register()
347 devm_of_led_get()
348
349MDIO
350 devm_mdiobus_alloc()
351 devm_mdiobus_alloc_size()
352 devm_mdiobus_register()
353 devm_of_mdiobus_register()
354
355MEM
356 devm_free_pages()
357 devm_get_free_pages()
358 devm_kasprintf()
359 devm_kcalloc()
360 devm_kfree()
361 devm_kmalloc()
362 devm_kmalloc_array()
363 devm_kmemdup()
364 devm_krealloc()
365 devm_krealloc_array()
366 devm_kstrdup()
367 devm_kstrdup_const()
368 devm_kvasprintf()
369 devm_kzalloc()
370
371MFD
372 devm_mfd_add_devices()
373
374MUX
375 devm_mux_chip_alloc()
376 devm_mux_chip_register()
377 devm_mux_control_get()
378 devm_mux_state_get()
379
380NET
381 devm_alloc_etherdev()
382 devm_alloc_etherdev_mqs()
383 devm_register_netdev()
384
385PER-CPU MEM
386 devm_alloc_percpu()
387
388PCI
389 devm_pci_alloc_host_bridge() : managed PCI host bridge allocation
390 devm_pci_remap_cfgspace() : ioremap PCI configuration space
391 devm_pci_remap_cfg_resource() : ioremap PCI configuration space resource
392
393 pcim_enable_device() : after success, the PCI device gets disabled automatically on driver detach
394 pcim_iomap() : do iomap() on a single BAR
395 pcim_iomap_regions() : do request_region() and iomap() on multiple BARs
396 pcim_iomap_table() : array of mapped addresses indexed by BAR
397 pcim_iounmap() : do iounmap() on a single BAR
398 pcim_pin_device() : keep PCI device enabled after release
399 pcim_set_mwi() : enable Memory-Write-Invalidate PCI transaction
400
401PHY
402 devm_usb_get_phy()
403 devm_usb_get_phy_by_node()
404 devm_usb_get_phy_by_phandle()
405
406PINCTRL
407 devm_pinctrl_get()
408 devm_pinctrl_put()
409 devm_pinctrl_get_select()
410 devm_pinctrl_register()
411 devm_pinctrl_register_and_init()
412
413POWER
414 devm_reboot_mode_register()
415 devm_reboot_mode_unregister()
416
417PWM
418 devm_pwmchip_alloc()
419 devm_pwmchip_add()
420 devm_pwm_get()
421 devm_fwnode_pwm_get()
422
423REGULATOR
424 devm_regulator_bulk_register_supply_alias()
425 devm_regulator_bulk_get()
426 devm_regulator_bulk_get_const()
427 devm_regulator_bulk_get_enable()
428 devm_regulator_bulk_put()
429 devm_regulator_get()
430 devm_regulator_get_enable()
431 devm_regulator_get_enable_read_voltage()
432 devm_regulator_get_enable_optional()
433 devm_regulator_get_exclusive()
434 devm_regulator_get_optional()
435 devm_regulator_irq_helper()
436 devm_regulator_put()
437 devm_regulator_register()
438 devm_regulator_register_notifier()
439 devm_regulator_register_supply_alias()
440 devm_regulator_unregister_notifier()
441
442RESET
443 devm_reset_control_get()
444 devm_reset_controller_register()
445
446RTC
447 devm_rtc_device_register()
448 devm_rtc_allocate_device()
449 devm_rtc_register_device()
450 devm_rtc_nvmem_register()
451
452SERDEV
453 devm_serdev_device_open()
454
455SLAVE DMA ENGINE
456 devm_acpi_dma_controller_register()
457
458SPI
459 devm_spi_alloc_host()
460 devm_spi_alloc_target()
461 devm_spi_optimize_message()
462 devm_spi_register_controller()
463 devm_spi_register_host()
464 devm_spi_register_target()
465
466WATCHDOG
467 devm_watchdog_register_device()
468
469WORKQUEUE
470 devm_alloc_workqueue()
471 devm_alloc_ordered_workqueue()