1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 ============================= 3 =============================
4 ACPI Based Device Enumeration 4 ACPI Based Device Enumeration
5 ============================= 5 =============================
6 6
7 ACPI 5 introduced a set of new resources (Uart 7 ACPI 5 introduced a set of new resources (UartTSerialBus, I2cSerialBus,
8 SpiSerialBus, GpioIo and GpioInt) which can be 8 SpiSerialBus, GpioIo and GpioInt) which can be used in enumerating slave
9 devices behind serial bus controllers. 9 devices behind serial bus controllers.
10 10
11 In addition we are starting to see peripherals 11 In addition we are starting to see peripherals integrated in the
12 SoC/Chipset to appear only in ACPI namespace. 12 SoC/Chipset to appear only in ACPI namespace. These are typically devices
13 that are accessed through memory-mapped regist 13 that are accessed through memory-mapped registers.
14 14
15 In order to support this and re-use the existi 15 In order to support this and re-use the existing drivers as much as
16 possible we decided to do following: 16 possible we decided to do following:
17 17
18 - Devices that have no bus connector resourc 18 - Devices that have no bus connector resource are represented as
19 platform devices. 19 platform devices.
20 20
21 - Devices behind real busses where there is 21 - Devices behind real busses where there is a connector resource
22 are represented as struct spi_device or st !! 22 are represented as struct spi_device or struct i2c_device
23 that standard UARTs are not busses so ther !! 23 (standard UARTs are not busses so there is no struct uart_device).
24 although some of them may be represented b <<
25 24
26 As both ACPI and Device Tree represent a tree 25 As both ACPI and Device Tree represent a tree of devices (and their
27 resources) this implementation follows the Dev 26 resources) this implementation follows the Device Tree way as much as
28 possible. 27 possible.
29 28
30 The ACPI implementation enumerates devices beh !! 29 The ACPI implementation enumerates devices behind busses (platform, SPI and
31 I2C, and in some cases UART), creates the phys !! 30 I2C), creates the physical devices and binds them to their ACPI handle in
32 to their ACPI handle in the ACPI namespace. !! 31 the ACPI namespace.
33 32
34 This means that when ACPI_HANDLE(dev) returns 33 This means that when ACPI_HANDLE(dev) returns non-NULL the device was
35 enumerated from ACPI namespace. This handle ca 34 enumerated from ACPI namespace. This handle can be used to extract other
36 device-specific configuration. There is an exa 35 device-specific configuration. There is an example of this below.
37 36
38 Platform bus support 37 Platform bus support
39 ==================== 38 ====================
40 39
41 Since we are using platform devices to represe 40 Since we are using platform devices to represent devices that are not
42 connected to any physical bus we only need to 41 connected to any physical bus we only need to implement a platform driver
43 for the device and add supported ACPI IDs. If 42 for the device and add supported ACPI IDs. If this same IP-block is used on
44 some other non-ACPI platform, the driver might 43 some other non-ACPI platform, the driver might work out of the box or needs
45 some minor changes. 44 some minor changes.
46 45
47 Adding ACPI support for an existing driver sho 46 Adding ACPI support for an existing driver should be pretty
48 straightforward. Here is the simplest example: 47 straightforward. Here is the simplest example::
49 48
>> 49 #ifdef CONFIG_ACPI
50 static const struct acpi_device_id myd 50 static const struct acpi_device_id mydrv_acpi_match[] = {
51 /* ACPI IDs here */ 51 /* ACPI IDs here */
52 { } 52 { }
53 }; 53 };
54 MODULE_DEVICE_TABLE(acpi, mydrv_acpi_m 54 MODULE_DEVICE_TABLE(acpi, mydrv_acpi_match);
>> 55 #endif
55 56
56 static struct platform_driver my_drive 57 static struct platform_driver my_driver = {
57 ... 58 ...
58 .driver = { 59 .driver = {
59 .acpi_match_table = my !! 60 .acpi_match_table = ACPI_PTR(mydrv_acpi_match),
60 }, 61 },
61 }; 62 };
62 63
63 If the driver needs to perform more complex in 64 If the driver needs to perform more complex initialization like getting and
64 configuring GPIOs it can get its ACPI handle a 65 configuring GPIOs it can get its ACPI handle and extract this information
65 from ACPI tables. 66 from ACPI tables.
66 67
67 ACPI device objects <<
68 =================== <<
69 <<
70 Generally speaking, there are two categories o <<
71 ACPI is used as an interface between the platf <<
72 that can be discovered and enumerated natively <<
73 the specific bus that they are on (for example <<
74 without the platform firmware assistance, and <<
75 by the platform firmware so that they can be d <<
76 known to the platform firmware, regardless of <<
77 there can be a corresponding ACPI device objec <<
78 case the Linux kernel will create a struct acp <<
79 that device. <<
80 <<
81 Those struct acpi_device objects are never use <<
82 discoverable devices, because they are represe <<
83 objects (for example, struct pci_dev for PCI d <<
84 device drivers (the corresponding struct acpi_ <<
85 an additional source of information on the con <<
86 Moreover, the core ACPI device enumeration cod <<
87 objects for the majority of devices that are d <<
88 help of the platform firmware and those platfo <<
89 by platform drivers in direct analogy with the <<
90 case. Therefore it is logically inconsistent <<
91 drivers to struct acpi_device objects, includi <<
92 discovered with the help of the platform firmw <<
93 <<
94 Historically, ACPI drivers that bound directly <<
95 were implemented for some devices enumerated w <<
96 firmware, but this is not recommended for any <<
97 platform device objects are created for those <<
98 exceptions that are not relevant here) and so <<
99 for handling them, even though the correspondi <<
100 only source of device configuration informatio <<
101 <<
102 For every device having a corresponding struct <<
103 to it is returned by the ACPI_COMPANION() macr <<
104 get to the device configuration information st <<
105 this way. Accordingly, struct acpi_device can <<
106 interface between the kernel and the ACPI Name <<
107 other types (for example, struct pci_dev or st <<
108 for interacting with the rest of the system. <<
109 <<
110 DMA support 68 DMA support
111 =========== 69 ===========
112 70
113 DMA controllers enumerated via ACPI should be 71 DMA controllers enumerated via ACPI should be registered in the system to
114 provide generic access to their resources. For 72 provide generic access to their resources. For example, a driver that would
115 like to be accessible to slave devices via gen 73 like to be accessible to slave devices via generic API call
116 dma_request_chan() must register itself at the 74 dma_request_chan() must register itself at the end of the probe function like
117 this:: 75 this::
118 76
119 err = devm_acpi_dma_controller_registe 77 err = devm_acpi_dma_controller_register(dev, xlate_func, dw);
120 /* Handle the error if it's not a case 78 /* Handle the error if it's not a case of !CONFIG_ACPI */
121 79
122 and implement custom xlate function if needed 80 and implement custom xlate function if needed (usually acpi_dma_simple_xlate()
123 is enough) which converts the FixedDMA resourc 81 is enough) which converts the FixedDMA resource provided by struct
124 acpi_dma_spec into the corresponding DMA chann 82 acpi_dma_spec into the corresponding DMA channel. A piece of code for that case
125 could look like:: 83 could look like::
126 84
127 #ifdef CONFIG_ACPI 85 #ifdef CONFIG_ACPI
128 struct filter_args { 86 struct filter_args {
129 /* Provide necessary informati 87 /* Provide necessary information for the filter_func */
130 ... 88 ...
131 }; 89 };
132 90
133 static bool filter_func(struct dma_cha 91 static bool filter_func(struct dma_chan *chan, void *param)
134 { 92 {
135 /* Choose the proper channel * 93 /* Choose the proper channel */
136 ... 94 ...
137 } 95 }
138 96
139 static struct dma_chan *xlate_func(str 97 static struct dma_chan *xlate_func(struct acpi_dma_spec *dma_spec,
140 struct acpi_dma *adma) 98 struct acpi_dma *adma)
141 { 99 {
142 dma_cap_mask_t cap; 100 dma_cap_mask_t cap;
143 struct filter_args args; 101 struct filter_args args;
144 102
145 /* Prepare arguments for filte 103 /* Prepare arguments for filter_func */
146 ... 104 ...
147 return dma_request_channel(cap 105 return dma_request_channel(cap, filter_func, &args);
148 } 106 }
149 #else 107 #else
150 static struct dma_chan *xlate_func(str 108 static struct dma_chan *xlate_func(struct acpi_dma_spec *dma_spec,
151 struct acpi_dma *adma) 109 struct acpi_dma *adma)
152 { 110 {
153 return NULL; 111 return NULL;
154 } 112 }
155 #endif 113 #endif
156 114
157 dma_request_chan() will call xlate_func() for 115 dma_request_chan() will call xlate_func() for each registered DMA controller.
158 In the xlate function the proper channel must 116 In the xlate function the proper channel must be chosen based on
159 information in struct acpi_dma_spec and the pr 117 information in struct acpi_dma_spec and the properties of the controller
160 provided by struct acpi_dma. 118 provided by struct acpi_dma.
161 119
162 Clients must call dma_request_chan() with the 120 Clients must call dma_request_chan() with the string parameter that corresponds
163 to a specific FixedDMA resource. By default "t 121 to a specific FixedDMA resource. By default "tx" means the first entry of the
164 FixedDMA resource array, "rx" means the second 122 FixedDMA resource array, "rx" means the second entry. The table below shows a
165 layout:: 123 layout::
166 124
167 Device (I2C0) 125 Device (I2C0)
168 { 126 {
169 ... 127 ...
170 Method (_CRS, 0, NotSerialized 128 Method (_CRS, 0, NotSerialized)
171 { 129 {
172 Name (DBUF, ResourceTe 130 Name (DBUF, ResourceTemplate ()
173 { 131 {
174 FixedDMA (0x00 132 FixedDMA (0x0018, 0x0004, Width32bit, _Y48)
175 FixedDMA (0x00 133 FixedDMA (0x0019, 0x0005, Width32bit, )
176 }) 134 })
177 ... 135 ...
178 } 136 }
179 } 137 }
180 138
181 So, the FixedDMA with request line 0x0018 is " 139 So, the FixedDMA with request line 0x0018 is "tx" and next one is "rx" in
182 this example. 140 this example.
183 141
184 In robust cases the client unfortunately needs 142 In robust cases the client unfortunately needs to call
185 acpi_dma_request_slave_chan_by_index() directl 143 acpi_dma_request_slave_chan_by_index() directly and therefore choose the
186 specific FixedDMA resource by its index. 144 specific FixedDMA resource by its index.
187 145
188 Named Interrupts <<
189 ================ <<
190 <<
191 Drivers enumerated via ACPI can have names to <<
192 which can be used to get the IRQ number in the <<
193 <<
194 The interrupt name can be listed in _DSD as 'i <<
195 should be listed as an array of strings which <<
196 resource in the ACPI table corresponding to it <<
197 <<
198 The table below shows an example of its usage: <<
199 <<
200 Device (DEV0) { <<
201 ... <<
202 Name (_CRS, ResourceTemplate() { <<
203 ... <<
204 Interrupt (ResourceConsumer, Level <<
205 0x20, <<
206 0x24 <<
207 } <<
208 }) <<
209 <<
210 Name (_DSD, Package () { <<
211 ToUUID("daffd814-6eba-4d8c-8a91-bc <<
212 Package () { <<
213 Package () { "interrupt-names" <<
214 } <<
215 ... <<
216 }) <<
217 } <<
218 <<
219 The interrupt name 'default' will correspond t <<
220 resource and 'alert' to 0x24. Note that only t <<
221 is mapped and not GpioInt() or similar. <<
222 <<
223 The driver can call the function - fwnode_irq_ <<
224 and interrupt name as arguments to get the cor <<
225 <<
226 SPI serial bus support 146 SPI serial bus support
227 ====================== 147 ======================
228 148
229 Slave devices behind SPI bus have SpiSerialBus 149 Slave devices behind SPI bus have SpiSerialBus resource attached to them.
230 This is extracted automatically by the SPI cor 150 This is extracted automatically by the SPI core and the slave devices are
231 enumerated once spi_register_master() is calle 151 enumerated once spi_register_master() is called by the bus driver.
232 152
233 Here is what the ACPI namespace for a SPI slav 153 Here is what the ACPI namespace for a SPI slave might look like::
234 154
235 Device (EEP0) 155 Device (EEP0)
236 { 156 {
237 Name (_ADR, 1) 157 Name (_ADR, 1)
238 Name (_CID, Package () { !! 158 Name (_CID, Package() {
239 "ATML0025", 159 "ATML0025",
240 "AT25", 160 "AT25",
241 }) 161 })
242 ... 162 ...
243 Method (_CRS, 0, NotSerialized 163 Method (_CRS, 0, NotSerialized)
244 { 164 {
245 SPISerialBus(1, Polari 165 SPISerialBus(1, PolarityLow, FourWireMode, 8,
246 ControllerInit 166 ControllerInitiated, 1000000, ClockPolarityLow,
247 ClockPhaseFirs 167 ClockPhaseFirst, "\\_SB.PCI0.SPI1",)
248 } 168 }
249 ... 169 ...
250 170
251 The SPI device drivers only need to add ACPI I !! 171 The SPI device drivers only need to add ACPI IDs in a similar way than with
252 the platform device drivers. Below is an examp 172 the platform device drivers. Below is an example where we add ACPI support
253 to at25 SPI eeprom driver (this is meant for t 173 to at25 SPI eeprom driver (this is meant for the above ACPI snippet)::
254 174
>> 175 #ifdef CONFIG_ACPI
255 static const struct acpi_device_id at2 176 static const struct acpi_device_id at25_acpi_match[] = {
256 { "AT25", 0 }, 177 { "AT25", 0 },
257 { } !! 178 { },
258 }; 179 };
259 MODULE_DEVICE_TABLE(acpi, at25_acpi_ma 180 MODULE_DEVICE_TABLE(acpi, at25_acpi_match);
>> 181 #endif
260 182
261 static struct spi_driver at25_driver = 183 static struct spi_driver at25_driver = {
262 .driver = { 184 .driver = {
263 ... 185 ...
264 .acpi_match_table = at !! 186 .acpi_match_table = ACPI_PTR(at25_acpi_match),
265 }, 187 },
266 }; 188 };
267 189
268 Note that this driver actually needs more info 190 Note that this driver actually needs more information like page size of the
269 eeprom, etc. This information can be passed vi !! 191 eeprom etc. but at the time writing this there is no standard way of
>> 192 passing those. One idea is to return this in _DSM method like::
270 193
271 Device (EEP0) 194 Device (EEP0)
272 { 195 {
273 ... 196 ...
274 Name (_DSD, Package () !! 197 Method (_DSM, 4, NotSerialized)
275 { 198 {
276 ToUUID("daffd814-6eba- !! 199 Store (Package (6)
277 Package () <<
278 { 200 {
279 Package () { " !! 201 "byte-len", 1024,
280 Package () { " !! 202 "addr-mode", 2,
281 Package () { " !! 203 "page-size, 32
282 } !! 204 }, Local0)
283 }) !! 205
284 } !! 206 // Check UUIDs etc.
>> 207
>> 208 Return (Local0)
>> 209 }
>> 210
>> 211 Then the at25 SPI driver can get this configuration by calling _DSM on its
>> 212 ACPI handle like::
285 213
286 Then the at25 SPI driver can get this configur !! 214 struct acpi_buffer output = { ACPI_ALLOCATE_BUFFER, NULL };
287 APIs during ->probe() phase like:: !! 215 struct acpi_object_list input;
>> 216 acpi_status status;
288 217
289 err = device_property_read_u32(dev, "s !! 218 /* Fill in the input buffer */
290 if (err) !! 219
291 ...error handling... !! 220 status = acpi_evaluate_object(ACPI_HANDLE(&spi->dev), "_DSM",
292 !! 221 &input, &output);
293 err = device_property_read_u32(dev, "p !! 222 if (ACPI_FAILURE(status))
294 if (err) !! 223 /* Handle the error */
295 ...error handling... !! 224
296 !! 225 /* Extract the data here */
297 err = device_property_read_u32(dev, "a !! 226
298 if (err) !! 227 kfree(output.pointer);
299 ...error handling... <<
300 228
301 I2C serial bus support 229 I2C serial bus support
302 ====================== 230 ======================
303 231
304 The slaves behind I2C bus controller only need 232 The slaves behind I2C bus controller only need to add the ACPI IDs like
305 with the platform and SPI drivers. The I2C cor 233 with the platform and SPI drivers. The I2C core automatically enumerates
306 any slave devices behind the controller device 234 any slave devices behind the controller device once the adapter is
307 registered. 235 registered.
308 236
309 Below is an example of how to add ACPI support 237 Below is an example of how to add ACPI support to the existing mpu3050
310 input driver:: 238 input driver::
311 239
>> 240 #ifdef CONFIG_ACPI
312 static const struct acpi_device_id mpu 241 static const struct acpi_device_id mpu3050_acpi_match[] = {
313 { "MPU3050", 0 }, 242 { "MPU3050", 0 },
314 { } !! 243 { },
315 }; 244 };
316 MODULE_DEVICE_TABLE(acpi, mpu3050_acpi 245 MODULE_DEVICE_TABLE(acpi, mpu3050_acpi_match);
>> 246 #endif
317 247
318 static struct i2c_driver mpu3050_i2c_d 248 static struct i2c_driver mpu3050_i2c_driver = {
319 .driver = { 249 .driver = {
320 .name = "mpu3050", 250 .name = "mpu3050",
>> 251 .owner = THIS_MODULE,
321 .pm = &mpu3050_pm, 252 .pm = &mpu3050_pm,
322 .of_match_table = mpu3 253 .of_match_table = mpu3050_of_match,
323 .acpi_match_table = mp !! 254 .acpi_match_table = ACPI_PTR(mpu3050_acpi_match),
324 }, 255 },
325 .probe = mpu3050_prob 256 .probe = mpu3050_probe,
326 .remove = mpu3050_remo 257 .remove = mpu3050_remove,
327 .id_table = mpu3050_ids, 258 .id_table = mpu3050_ids,
328 }; 259 };
329 module_i2c_driver(mpu3050_i2c_driver); <<
330 <<
331 Reference to PWM device <<
332 ======================= <<
333 <<
334 Sometimes a device can be a consumer of PWM ch <<
335 to know which one. To provide this mapping the <<
336 introduced, i.e.:: <<
337 <<
338 Device (DEV) <<
339 { <<
340 Name (_DSD, Package () <<
341 { <<
342 ToUUID("daffd814-6eba-4d8c-8a91-bc <<
343 Package () { <<
344 Package () { "compatible", Pac <<
345 Package () { "label", "alarm-l <<
346 Package () { "pwms", <<
347 Package () { <<
348 "\\_SB.PCI0.PWM", // <<
349 0, // <<
350 600000000, // <<
351 0, // <<
352 } <<
353 } <<
354 } <<
355 }) <<
356 ... <<
357 } <<
358 <<
359 In the above example the PWM-based LED driver <<
360 of \_SB.PCI0.PWM device with initial period se <<
361 value is given in nanoseconds). <<
362 260
363 GPIO support 261 GPIO support
364 ============ 262 ============
365 263
366 ACPI 5 introduced two new resources to describ 264 ACPI 5 introduced two new resources to describe GPIO connections: GpioIo
367 and GpioInt. These resources can be used to pa 265 and GpioInt. These resources can be used to pass GPIO numbers used by
368 the device to the driver. ACPI 5.1 extended th 266 the device to the driver. ACPI 5.1 extended this with _DSD (Device
369 Specific Data) which made it possible to name 267 Specific Data) which made it possible to name the GPIOs among other things.
370 268
371 For example:: 269 For example::
372 270
373 Device (DEV) 271 Device (DEV)
374 { 272 {
375 Method (_CRS, 0, NotSerialized 273 Method (_CRS, 0, NotSerialized)
376 { 274 {
377 Name (SBUF, ResourceTe 275 Name (SBUF, ResourceTemplate()
378 { 276 {
>> 277 ...
379 // Used to pow 278 // Used to power on/off the device
380 GpioIo (Exclus !! 279 GpioIo (Exclusive, PullDefault, 0x0000, 0x0000,
381 "\\_SB !! 280 IoRestrictionOutputOnly, "\\_SB.PCI0.GPI0",
>> 281 0x00, ResourceConsumer,,)
>> 282 {
>> 283 // Pin List
>> 284 0x0055
>> 285 }
382 286
383 // Interrupt f 287 // Interrupt for the device
384 GpioInt (Edge, !! 288 GpioInt (Edge, ActiveHigh, ExclusiveAndWake, PullNone,
385 "\\_S !! 289 0x0000, "\\_SB.PCI0.GPI0", 0x00, ResourceConsumer,,)
>> 290 {
>> 291 // Pin list
>> 292 0x0058
>> 293 }
>> 294
>> 295 ...
>> 296
386 } 297 }
387 298
388 Return (SBUF) 299 Return (SBUF)
389 } 300 }
390 301
391 // ACPI 5.1 _DSD used for nami 302 // ACPI 5.1 _DSD used for naming the GPIOs
392 Name (_DSD, Package () 303 Name (_DSD, Package ()
393 { 304 {
394 ToUUID("daffd814-6eba- 305 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
395 Package () 306 Package ()
396 { 307 {
397 Package () { " !! 308 Package () {"power-gpios", Package() {^DEV, 0, 0, 0 }},
398 Package () { " !! 309 Package () {"irq-gpios", Package() {^DEV, 1, 0, 0 }},
399 } 310 }
400 }) 311 })
401 ... 312 ...
402 } <<
403 313
404 These GPIO numbers are controller relative and 314 These GPIO numbers are controller relative and path "\\_SB.PCI0.GPI0"
405 specifies the path to the controller. In order 315 specifies the path to the controller. In order to use these GPIOs in Linux
406 we need to translate them to the corresponding 316 we need to translate them to the corresponding Linux GPIO descriptors.
407 317
408 There is a standard GPIO API for that and it i !! 318 There is a standard GPIO API for that and is documented in
409 Documentation/admin-guide/gpio/. 319 Documentation/admin-guide/gpio/.
410 320
411 In the above example we can get the correspond 321 In the above example we can get the corresponding two GPIO descriptors with
412 a code like this:: 322 a code like this::
413 323
414 #include <linux/gpio/consumer.h> 324 #include <linux/gpio/consumer.h>
415 ... 325 ...
416 326
417 struct gpio_desc *irq_desc, *power_des 327 struct gpio_desc *irq_desc, *power_desc;
418 328
419 irq_desc = gpiod_get(dev, "irq"); 329 irq_desc = gpiod_get(dev, "irq");
420 if (IS_ERR(irq_desc)) 330 if (IS_ERR(irq_desc))
421 /* handle error */ 331 /* handle error */
422 332
423 power_desc = gpiod_get(dev, "power"); 333 power_desc = gpiod_get(dev, "power");
424 if (IS_ERR(power_desc)) 334 if (IS_ERR(power_desc))
425 /* handle error */ 335 /* handle error */
426 336
427 /* Now we can use the GPIO descriptors 337 /* Now we can use the GPIO descriptors */
428 338
429 There are also devm_* versions of these functi 339 There are also devm_* versions of these functions which release the
430 descriptors once the device is released. 340 descriptors once the device is released.
431 341
432 See Documentation/firmware-guide/acpi/gpio-pro !! 342 See Documentation/firmware-guide/acpi/gpio-properties.rst for more information about the
433 about the _DSD binding related to GPIOs. !! 343 _DSD binding related to GPIOs.
434 <<
435 RS-485 support <<
436 ============== <<
437 <<
438 ACPI _DSD (Device Specific Data) can be used t <<
439 of UART. <<
440 <<
441 For example:: <<
442 <<
443 Device (DEV) <<
444 { <<
445 ... <<
446 <<
447 // ACPI 5.1 _DSD used for RS-4 <<
448 Name (_DSD, Package () <<
449 { <<
450 ToUUID("daffd814-6eba- <<
451 Package () <<
452 { <<
453 Package () {"r <<
454 Package () {"r <<
455 Package () {"r <<
456 } <<
457 }) <<
458 ... <<
459 344
460 MFD devices 345 MFD devices
461 =========== 346 ===========
462 347
463 The MFD devices register their children as pla 348 The MFD devices register their children as platform devices. For the child
464 devices there needs to be an ACPI handle that 349 devices there needs to be an ACPI handle that they can use to reference
465 parts of the ACPI namespace that relate to the 350 parts of the ACPI namespace that relate to them. In the Linux MFD subsystem
466 we provide two ways: 351 we provide two ways:
467 352
468 - The children share the parent ACPI handle. 353 - The children share the parent ACPI handle.
469 - The MFD cell can specify the ACPI id of th 354 - The MFD cell can specify the ACPI id of the device.
470 355
471 For the first case, the MFD drivers do not nee 356 For the first case, the MFD drivers do not need to do anything. The
472 resulting child platform device will have its 357 resulting child platform device will have its ACPI_COMPANION() set to point
473 to the parent device. 358 to the parent device.
474 359
475 If the ACPI namespace has a device that we can 360 If the ACPI namespace has a device that we can match using an ACPI id or ACPI
476 adr, the cell should be set like:: 361 adr, the cell should be set like::
477 362
478 static struct mfd_cell_acpi_match my_s 363 static struct mfd_cell_acpi_match my_subdevice_cell_acpi_match = {
479 .pnpid = "XYZ0001", 364 .pnpid = "XYZ0001",
480 .adr = 0, 365 .adr = 0,
481 }; 366 };
482 367
483 static struct mfd_cell my_subdevice_ce 368 static struct mfd_cell my_subdevice_cell = {
484 .name = "my_subdevice", 369 .name = "my_subdevice",
485 /* set the resources relative 370 /* set the resources relative to the parent */
486 .acpi_match = &my_subdevice_ce 371 .acpi_match = &my_subdevice_cell_acpi_match,
487 }; 372 };
488 373
489 The ACPI id "XYZ0001" is then used to lookup a 374 The ACPI id "XYZ0001" is then used to lookup an ACPI device directly under
490 the MFD device and if found, that ACPI compani 375 the MFD device and if found, that ACPI companion device is bound to the
491 resulting child platform device. 376 resulting child platform device.
492 377
493 Device Tree namespace link device ID 378 Device Tree namespace link device ID
494 ==================================== 379 ====================================
495 380
496 The Device Tree protocol uses device identific 381 The Device Tree protocol uses device identification based on the "compatible"
497 property whose value is a string or an array o 382 property whose value is a string or an array of strings recognized as device
498 identifiers by drivers and the driver core. T 383 identifiers by drivers and the driver core. The set of all those strings may be
499 regarded as a device identification namespace 384 regarded as a device identification namespace analogous to the ACPI/PNP device
500 ID namespace. Consequently, in principle it s 385 ID namespace. Consequently, in principle it should not be necessary to allocate
501 a new (and arguably redundant) ACPI/PNP device 386 a new (and arguably redundant) ACPI/PNP device ID for a devices with an existing
502 identification string in the Device Tree (DT) 387 identification string in the Device Tree (DT) namespace, especially if that ID
503 is only needed to indicate that a given device 388 is only needed to indicate that a given device is compatible with another one,
504 presumably having a matching driver in the ker 389 presumably having a matching driver in the kernel already.
505 390
506 In ACPI, the device identification object call 391 In ACPI, the device identification object called _CID (Compatible ID) is used to
507 list the IDs of devices the given one is compa 392 list the IDs of devices the given one is compatible with, but those IDs must
508 belong to one of the namespaces prescribed by 393 belong to one of the namespaces prescribed by the ACPI specification (see
509 Section 6.1.2 of ACPI 6.0 for details) and the 394 Section 6.1.2 of ACPI 6.0 for details) and the DT namespace is not one of them.
510 Moreover, the specification mandates that eith 395 Moreover, the specification mandates that either a _HID or an _ADR identification
511 object be present for all ACPI objects represe 396 object be present for all ACPI objects representing devices (Section 6.1 of ACPI
512 6.0). For non-enumerable bus types that objec 397 6.0). For non-enumerable bus types that object must be _HID and its value must
513 be a device ID from one of the namespaces pres 398 be a device ID from one of the namespaces prescribed by the specification too.
514 399
515 The special DT namespace link device ID, PRP00 400 The special DT namespace link device ID, PRP0001, provides a means to use the
516 existing DT-compatible device identification i 401 existing DT-compatible device identification in ACPI and to satisfy the above
517 requirements following from the ACPI specifica 402 requirements following from the ACPI specification at the same time. Namely,
518 if PRP0001 is returned by _HID, the ACPI subsy 403 if PRP0001 is returned by _HID, the ACPI subsystem will look for the
519 "compatible" property in the device object's _ 404 "compatible" property in the device object's _DSD and will use the value of that
520 property to identify the corresponding device 405 property to identify the corresponding device in analogy with the original DT
521 device identification algorithm. If the "comp 406 device identification algorithm. If the "compatible" property is not present
522 or its value is not valid, the device will not 407 or its value is not valid, the device will not be enumerated by the ACPI
523 subsystem. Otherwise, it will be enumerated a 408 subsystem. Otherwise, it will be enumerated automatically as a platform device
524 (except when an I2C or SPI link from the devic 409 (except when an I2C or SPI link from the device to its parent is present, in
525 which case the ACPI core will leave the device 410 which case the ACPI core will leave the device enumeration to the parent's
526 driver) and the identification strings from th 411 driver) and the identification strings from the "compatible" property value will
527 be used to find a driver for the device along 412 be used to find a driver for the device along with the device IDs listed by _CID
528 (if present). 413 (if present).
529 414
530 Analogously, if PRP0001 is present in the list 415 Analogously, if PRP0001 is present in the list of device IDs returned by _CID,
531 the identification strings listed by the "comp 416 the identification strings listed by the "compatible" property value (if present
532 and valid) will be used to look for a driver m 417 and valid) will be used to look for a driver matching the device, but in that
533 case their relative priority with respect to t 418 case their relative priority with respect to the other device IDs listed by
534 _HID and _CID depends on the position of PRP00 419 _HID and _CID depends on the position of PRP0001 in the _CID return package.
535 Specifically, the device IDs returned by _HID 420 Specifically, the device IDs returned by _HID and preceding PRP0001 in the _CID
536 return package will be checked first. Also in 421 return package will be checked first. Also in that case the bus type the device
537 will be enumerated to depends on the device ID 422 will be enumerated to depends on the device ID returned by _HID.
538 423
539 For example, the following ACPI sample might b 424 For example, the following ACPI sample might be used to enumerate an lm75-type
540 I2C temperature sensor and match it to the dri 425 I2C temperature sensor and match it to the driver using the Device Tree
541 namespace link:: 426 namespace link::
542 427
543 Device (TMP0) 428 Device (TMP0)
544 { 429 {
545 Name (_HID, "PRP0001") 430 Name (_HID, "PRP0001")
546 Name (_DSD, Package () { !! 431 Name (_DSD, Package() {
547 ToUUID("daffd814-6eba- 432 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
548 Package () { 433 Package () {
549 Package () { " !! 434 Package (2) { "compatible", "ti,tmp75" },
550 } 435 }
551 }) 436 })
552 Method (_CRS, 0, Serialized) 437 Method (_CRS, 0, Serialized)
553 { 438 {
554 Name (SBUF, ResourceTe 439 Name (SBUF, ResourceTemplate ()
555 { 440 {
556 I2cSerialBusV2 441 I2cSerialBusV2 (0x48, ControllerInitiated,
557 400000 442 400000, AddressingMode7Bit,
558 "\\_SB 443 "\\_SB.PCI0.I2C1", 0x00,
559 Resour 444 ResourceConsumer, , Exclusive,)
560 }) 445 })
561 Return (SBUF) 446 Return (SBUF)
562 } 447 }
563 } 448 }
564 449
565 It is valid to define device objects with a _H 450 It is valid to define device objects with a _HID returning PRP0001 and without
566 the "compatible" property in the _DSD or a _CI 451 the "compatible" property in the _DSD or a _CID as long as one of their
567 ancestors provides a _DSD with a valid "compat 452 ancestors provides a _DSD with a valid "compatible" property. Such device
568 objects are then simply regarded as additional 453 objects are then simply regarded as additional "blocks" providing hierarchical
569 configuration information to the driver of the 454 configuration information to the driver of the composite ancestor device.
570 455
571 However, PRP0001 can only be returned from eit 456 However, PRP0001 can only be returned from either _HID or _CID of a device
572 object if all of the properties returned by th 457 object if all of the properties returned by the _DSD associated with it (either
573 the _DSD of the device object itself or the _D 458 the _DSD of the device object itself or the _DSD of its ancestor in the
574 "composite device" case described above) can b 459 "composite device" case described above) can be used in the ACPI environment.
575 Otherwise, the _DSD itself is regarded as inva 460 Otherwise, the _DSD itself is regarded as invalid and therefore the "compatible"
576 property returned by it is meaningless. 461 property returned by it is meaningless.
577 462
578 Refer to Documentation/firmware-guide/acpi/DSD !! 463 Refer to :doc:`DSD-properties-rules` for more information.
579 information. <<
580 464
581 PCI hierarchy representation 465 PCI hierarchy representation
582 ============================ 466 ============================
583 467
584 Sometimes it could be useful to enumerate a PC !! 468 Sometimes could be useful to enumerate a PCI device, knowing its position on the
585 the PCI bus. !! 469 PCI bus.
586 470
587 For example, some systems use PCI devices sold 471 For example, some systems use PCI devices soldered directly on the mother board,
588 in a fixed position (ethernet, Wi-Fi, serial p 472 in a fixed position (ethernet, Wi-Fi, serial ports, etc.). In this conditions it
589 is possible to refer to these PCI devices know 473 is possible to refer to these PCI devices knowing their position on the PCI bus
590 topology. 474 topology.
591 475
592 To identify a PCI device, a complete hierarchi 476 To identify a PCI device, a complete hierarchical description is required, from
593 the chipset root port to the final device, thr 477 the chipset root port to the final device, through all the intermediate
594 bridges/switches of the board. 478 bridges/switches of the board.
595 479
596 For example, let's assume we have a system wit !! 480 For example, let us assume to have a system with a PCIe serial port, an
597 Exar XR17V3521, soldered on the main board. Th 481 Exar XR17V3521, soldered on the main board. This UART chip also includes
598 16 GPIOs and we want to add the property ``gpi !! 482 16 GPIOs and we want to add the property ``gpio-line-names`` [1] to these pins.
599 In this case, the ``lspci`` output for this co 483 In this case, the ``lspci`` output for this component is::
600 484
601 07:00.0 Serial controller: Exar Corp. 485 07:00.0 Serial controller: Exar Corp. XR17V3521 Dual PCIe UART (rev 03)
602 486
603 The complete ``lspci`` output (manually reduce 487 The complete ``lspci`` output (manually reduced in length) is::
604 488
605 00:00.0 Host bridge: Intel Corp... Hos 489 00:00.0 Host bridge: Intel Corp... Host Bridge (rev 0d)
606 ... 490 ...
607 00:13.0 PCI bridge: Intel Corp... PCI 491 00:13.0 PCI bridge: Intel Corp... PCI Express Port A #1 (rev fd)
608 00:13.1 PCI bridge: Intel Corp... PCI 492 00:13.1 PCI bridge: Intel Corp... PCI Express Port A #2 (rev fd)
609 00:13.2 PCI bridge: Intel Corp... PCI 493 00:13.2 PCI bridge: Intel Corp... PCI Express Port A #3 (rev fd)
610 00:14.0 PCI bridge: Intel Corp... PCI 494 00:14.0 PCI bridge: Intel Corp... PCI Express Port B #1 (rev fd)
611 00:14.1 PCI bridge: Intel Corp... PCI 495 00:14.1 PCI bridge: Intel Corp... PCI Express Port B #2 (rev fd)
612 ... 496 ...
613 05:00.0 PCI bridge: Pericom Semiconduc 497 05:00.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
614 06:01.0 PCI bridge: Pericom Semiconduc 498 06:01.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
615 06:02.0 PCI bridge: Pericom Semiconduc 499 06:02.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
616 06:03.0 PCI bridge: Pericom Semiconduc 500 06:03.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
617 07:00.0 Serial controller: Exar Corp. 501 07:00.0 Serial controller: Exar Corp. XR17V3521 Dual PCIe UART (rev 03) <-- Exar
618 ... 502 ...
619 503
620 The bus topology is:: 504 The bus topology is::
621 505
622 -[0000:00]-+-00.0 506 -[0000:00]-+-00.0
623 ... 507 ...
624 +-13.0-[01]----00.0 508 +-13.0-[01]----00.0
625 +-13.1-[02]----00.0 509 +-13.1-[02]----00.0
626 +-13.2-[03]-- 510 +-13.2-[03]--
627 +-14.0-[04]----00.0 511 +-14.0-[04]----00.0
628 +-14.1-[05-09]----00.0-[06- 512 +-14.1-[05-09]----00.0-[06-09]--+-01.0-[07]----00.0 <-- Exar
629 | 513 | +-02.0-[08]----00.0
630 | 514 | \-03.0-[09]--
631 ... 515 ...
632 \-1f.1 516 \-1f.1
633 517
634 To describe this Exar device on the PCI bus, w 518 To describe this Exar device on the PCI bus, we must start from the ACPI name
635 of the chipset bridge (also called "root port" 519 of the chipset bridge (also called "root port") with address::
636 520
637 Bus: 0 - Device: 14 - Function: 1 521 Bus: 0 - Device: 14 - Function: 1
638 522
639 To find this information, it is necessary to d !! 523 To find this information is necessary disassemble the BIOS ACPI tables, in
640 in particular the DSDT (see also [2]_):: !! 524 particular the DSDT (see also [2])::
641 525
642 mkdir ~/tables/ 526 mkdir ~/tables/
643 cd ~/tables/ 527 cd ~/tables/
644 acpidump > acpidump 528 acpidump > acpidump
645 acpixtract -a acpidump 529 acpixtract -a acpidump
646 iasl -e ssdt?.* -d dsdt.dat 530 iasl -e ssdt?.* -d dsdt.dat
647 531
648 Now, in the dsdt.dsl, we have to search the de 532 Now, in the dsdt.dsl, we have to search the device whose address is related to
649 0x14 (device) and 0x01 (function). In this cas 533 0x14 (device) and 0x01 (function). In this case we can find the following
650 device:: 534 device::
651 535
652 Scope (_SB.PCI0) 536 Scope (_SB.PCI0)
653 { 537 {
654 ... other definitions follow ... 538 ... other definitions follow ...
655 Device (RP02) 539 Device (RP02)
656 { 540 {
657 Method (_ADR, 0, NotSe 541 Method (_ADR, 0, NotSerialized) // _ADR: Address
658 { 542 {
659 If ((RPA2 != Z 543 If ((RPA2 != Zero))
660 { 544 {
661 Return 545 Return (RPA2) /* \RPA2 */
662 } 546 }
663 Else 547 Else
664 { 548 {
665 Return 549 Return (0x00140001)
666 } 550 }
667 } 551 }
668 ... other definitions follow ... 552 ... other definitions follow ...
669 553
670 and the _ADR method [3]_ returns exactly the d !! 554 and the _ADR method [3] returns exactly the device/function couple that
671 we are looking for. With this information and 555 we are looking for. With this information and analyzing the above ``lspci``
672 output (both the devices list and the devices 556 output (both the devices list and the devices tree), we can write the following
673 ACPI description for the Exar PCIe UART, also 557 ACPI description for the Exar PCIe UART, also adding the list of its GPIO line
674 names:: 558 names::
675 559
676 Scope (_SB.PCI0.RP02) 560 Scope (_SB.PCI0.RP02)
677 { 561 {
678 Device (BRG1) //Bridge 562 Device (BRG1) //Bridge
679 { 563 {
680 Name (_ADR, 0x0000) 564 Name (_ADR, 0x0000)
681 565
682 Device (BRG2) //Bridge 566 Device (BRG2) //Bridge
683 { 567 {
684 Name (_ADR, 0x 568 Name (_ADR, 0x00010000)
685 569
686 Device (EXAR) 570 Device (EXAR)
687 { 571 {
688 Name ( 572 Name (_ADR, 0x0000)
689 573
690 Name ( 574 Name (_DSD, Package ()
691 { 575 {
692 576 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
693 577 Package ()
694 578 {
695 579 Package ()
696 580 {
697 581 "gpio-line-names",
698 582 Package ()
699 583 {
700 584 "mode_232",
701 585 "mode_422",
702 586 "mode_485",
703 587 "misc_1",
704 588 "misc_2",
705 589 "misc_3",
706 590 "",
707 591 "",
708 592 "aux_1",
709 593 "aux_2",
710 594 "aux_3",
711 595 }
712 596 }
713 597 }
714 }) 598 })
715 } 599 }
716 } 600 }
717 } 601 }
718 } 602 }
719 603
720 The location "_SB.PCI0.RP02" is obtained by th 604 The location "_SB.PCI0.RP02" is obtained by the above investigation in the
721 dsdt.dsl table, whereas the device names "BRG1 605 dsdt.dsl table, whereas the device names "BRG1", "BRG2" and "EXAR" are
722 created analyzing the position of the Exar UAR 606 created analyzing the position of the Exar UART in the PCI bus topology.
723 607
724 References 608 References
725 ========== 609 ==========
726 610
727 .. [1] Documentation/firmware-guide/acpi/gpio- !! 611 [1] Documentation/firmware-guide/acpi/gpio-properties.rst
728 612
729 .. [2] Documentation/admin-guide/acpi/initrd_t !! 613 [2] Documentation/admin-guide/acpi/initrd_table_override.rst
730 614
731 .. [3] ACPI Specifications, Version 6.3 - Para !! 615 [3] ACPI Specifications, Version 6.3 - Paragraph 6.1.1 _ADR Address)
732 https://uefi.org/sites/default/files/resou 616 https://uefi.org/sites/default/files/resources/ACPI_6_3_May16.pdf,
733 referenced 2020-11-18 617 referenced 2020-11-18
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