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_client. Note
23 that standard UARTs are not busses so ther 23 that standard UARTs are not busses so there is no struct uart_device,
24 although some of them may be represented b 24 although some of them may be represented by struct serdev_device.
25 25
26 As both ACPI and Device Tree represent a tree 26 As both ACPI and Device Tree represent a tree of devices (and their
27 resources) this implementation follows the Dev 27 resources) this implementation follows the Device Tree way as much as
28 possible. 28 possible.
29 29
30 The ACPI implementation enumerates devices beh 30 The ACPI implementation enumerates devices behind busses (platform, SPI,
31 I2C, and in some cases UART), creates the phys 31 I2C, and in some cases UART), creates the physical devices and binds them
32 to their ACPI handle in the ACPI namespace. 32 to their ACPI handle in the ACPI namespace.
33 33
34 This means that when ACPI_HANDLE(dev) returns 34 This means that when ACPI_HANDLE(dev) returns non-NULL the device was
35 enumerated from ACPI namespace. This handle ca 35 enumerated from ACPI namespace. This handle can be used to extract other
36 device-specific configuration. There is an exa 36 device-specific configuration. There is an example of this below.
37 37
38 Platform bus support 38 Platform bus support
39 ==================== 39 ====================
40 40
41 Since we are using platform devices to represe 41 Since we are using platform devices to represent devices that are not
42 connected to any physical bus we only need to 42 connected to any physical bus we only need to implement a platform driver
43 for the device and add supported ACPI IDs. If 43 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 44 some other non-ACPI platform, the driver might work out of the box or needs
45 some minor changes. 45 some minor changes.
46 46
47 Adding ACPI support for an existing driver sho 47 Adding ACPI support for an existing driver should be pretty
48 straightforward. Here is the simplest example: 48 straightforward. Here is the simplest example::
49 49
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 55
56 static struct platform_driver my_drive 56 static struct platform_driver my_driver = {
57 ... 57 ...
58 .driver = { 58 .driver = {
59 .acpi_match_table = my 59 .acpi_match_table = mydrv_acpi_match,
60 }, 60 },
61 }; 61 };
62 62
63 If the driver needs to perform more complex in 63 If the driver needs to perform more complex initialization like getting and
64 configuring GPIOs it can get its ACPI handle a 64 configuring GPIOs it can get its ACPI handle and extract this information
65 from ACPI tables. 65 from ACPI tables.
66 66
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 67 DMA support
111 =========== 68 ===========
112 69
113 DMA controllers enumerated via ACPI should be 70 DMA controllers enumerated via ACPI should be registered in the system to
114 provide generic access to their resources. For 71 provide generic access to their resources. For example, a driver that would
115 like to be accessible to slave devices via gen 72 like to be accessible to slave devices via generic API call
116 dma_request_chan() must register itself at the 73 dma_request_chan() must register itself at the end of the probe function like
117 this:: 74 this::
118 75
119 err = devm_acpi_dma_controller_registe 76 err = devm_acpi_dma_controller_register(dev, xlate_func, dw);
120 /* Handle the error if it's not a case 77 /* Handle the error if it's not a case of !CONFIG_ACPI */
121 78
122 and implement custom xlate function if needed 79 and implement custom xlate function if needed (usually acpi_dma_simple_xlate()
123 is enough) which converts the FixedDMA resourc 80 is enough) which converts the FixedDMA resource provided by struct
124 acpi_dma_spec into the corresponding DMA chann 81 acpi_dma_spec into the corresponding DMA channel. A piece of code for that case
125 could look like:: 82 could look like::
126 83
127 #ifdef CONFIG_ACPI 84 #ifdef CONFIG_ACPI
128 struct filter_args { 85 struct filter_args {
129 /* Provide necessary informati 86 /* Provide necessary information for the filter_func */
130 ... 87 ...
131 }; 88 };
132 89
133 static bool filter_func(struct dma_cha 90 static bool filter_func(struct dma_chan *chan, void *param)
134 { 91 {
135 /* Choose the proper channel * 92 /* Choose the proper channel */
136 ... 93 ...
137 } 94 }
138 95
139 static struct dma_chan *xlate_func(str 96 static struct dma_chan *xlate_func(struct acpi_dma_spec *dma_spec,
140 struct acpi_dma *adma) 97 struct acpi_dma *adma)
141 { 98 {
142 dma_cap_mask_t cap; 99 dma_cap_mask_t cap;
143 struct filter_args args; 100 struct filter_args args;
144 101
145 /* Prepare arguments for filte 102 /* Prepare arguments for filter_func */
146 ... 103 ...
147 return dma_request_channel(cap 104 return dma_request_channel(cap, filter_func, &args);
148 } 105 }
149 #else 106 #else
150 static struct dma_chan *xlate_func(str 107 static struct dma_chan *xlate_func(struct acpi_dma_spec *dma_spec,
151 struct acpi_dma *adma) 108 struct acpi_dma *adma)
152 { 109 {
153 return NULL; 110 return NULL;
154 } 111 }
155 #endif 112 #endif
156 113
157 dma_request_chan() will call xlate_func() for 114 dma_request_chan() will call xlate_func() for each registered DMA controller.
158 In the xlate function the proper channel must 115 In the xlate function the proper channel must be chosen based on
159 information in struct acpi_dma_spec and the pr 116 information in struct acpi_dma_spec and the properties of the controller
160 provided by struct acpi_dma. 117 provided by struct acpi_dma.
161 118
162 Clients must call dma_request_chan() with the 119 Clients must call dma_request_chan() with the string parameter that corresponds
163 to a specific FixedDMA resource. By default "t 120 to a specific FixedDMA resource. By default "tx" means the first entry of the
164 FixedDMA resource array, "rx" means the second 121 FixedDMA resource array, "rx" means the second entry. The table below shows a
165 layout:: 122 layout::
166 123
167 Device (I2C0) 124 Device (I2C0)
168 { 125 {
169 ... 126 ...
170 Method (_CRS, 0, NotSerialized 127 Method (_CRS, 0, NotSerialized)
171 { 128 {
172 Name (DBUF, ResourceTe 129 Name (DBUF, ResourceTemplate ()
173 { 130 {
174 FixedDMA (0x00 131 FixedDMA (0x0018, 0x0004, Width32bit, _Y48)
175 FixedDMA (0x00 132 FixedDMA (0x0019, 0x0005, Width32bit, )
176 }) 133 })
177 ... 134 ...
178 } 135 }
179 } 136 }
180 137
181 So, the FixedDMA with request line 0x0018 is " 138 So, the FixedDMA with request line 0x0018 is "tx" and next one is "rx" in
182 this example. 139 this example.
183 140
184 In robust cases the client unfortunately needs 141 In robust cases the client unfortunately needs to call
185 acpi_dma_request_slave_chan_by_index() directl 142 acpi_dma_request_slave_chan_by_index() directly and therefore choose the
186 specific FixedDMA resource by its index. 143 specific FixedDMA resource by its index.
187 144
188 Named Interrupts 145 Named Interrupts
189 ================ 146 ================
190 147
191 Drivers enumerated via ACPI can have names to 148 Drivers enumerated via ACPI can have names to interrupts in the ACPI table
192 which can be used to get the IRQ number in the 149 which can be used to get the IRQ number in the driver.
193 150
194 The interrupt name can be listed in _DSD as 'i 151 The interrupt name can be listed in _DSD as 'interrupt-names'. The names
195 should be listed as an array of strings which 152 should be listed as an array of strings which will map to the Interrupt()
196 resource in the ACPI table corresponding to it 153 resource in the ACPI table corresponding to its index.
197 154
198 The table below shows an example of its usage: 155 The table below shows an example of its usage::
199 156
200 Device (DEV0) { 157 Device (DEV0) {
201 ... 158 ...
202 Name (_CRS, ResourceTemplate() { 159 Name (_CRS, ResourceTemplate() {
203 ... 160 ...
204 Interrupt (ResourceConsumer, Level 161 Interrupt (ResourceConsumer, Level, ActiveHigh, Exclusive) {
205 0x20, 162 0x20,
206 0x24 163 0x24
207 } 164 }
208 }) 165 })
209 166
210 Name (_DSD, Package () { 167 Name (_DSD, Package () {
211 ToUUID("daffd814-6eba-4d8c-8a91-bc 168 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
212 Package () { 169 Package () {
213 Package () { "interrupt-names" 170 Package () { "interrupt-names", Package () { "default", "alert" } },
214 } 171 }
215 ... 172 ...
216 }) 173 })
217 } 174 }
218 175
219 The interrupt name 'default' will correspond t 176 The interrupt name 'default' will correspond to 0x20 in Interrupt()
220 resource and 'alert' to 0x24. Note that only t 177 resource and 'alert' to 0x24. Note that only the Interrupt() resource
221 is mapped and not GpioInt() or similar. 178 is mapped and not GpioInt() or similar.
222 179
223 The driver can call the function - fwnode_irq_ 180 The driver can call the function - fwnode_irq_get_byname() with the fwnode
224 and interrupt name as arguments to get the cor 181 and interrupt name as arguments to get the corresponding IRQ number.
225 182
226 SPI serial bus support 183 SPI serial bus support
227 ====================== 184 ======================
228 185
229 Slave devices behind SPI bus have SpiSerialBus 186 Slave devices behind SPI bus have SpiSerialBus resource attached to them.
230 This is extracted automatically by the SPI cor 187 This is extracted automatically by the SPI core and the slave devices are
231 enumerated once spi_register_master() is calle 188 enumerated once spi_register_master() is called by the bus driver.
232 189
233 Here is what the ACPI namespace for a SPI slav 190 Here is what the ACPI namespace for a SPI slave might look like::
234 191
235 Device (EEP0) 192 Device (EEP0)
236 { 193 {
237 Name (_ADR, 1) 194 Name (_ADR, 1)
238 Name (_CID, Package () { 195 Name (_CID, Package () {
239 "ATML0025", 196 "ATML0025",
240 "AT25", 197 "AT25",
241 }) 198 })
242 ... 199 ...
243 Method (_CRS, 0, NotSerialized 200 Method (_CRS, 0, NotSerialized)
244 { 201 {
245 SPISerialBus(1, Polari 202 SPISerialBus(1, PolarityLow, FourWireMode, 8,
246 ControllerInit 203 ControllerInitiated, 1000000, ClockPolarityLow,
247 ClockPhaseFirs 204 ClockPhaseFirst, "\\_SB.PCI0.SPI1",)
248 } 205 }
249 ... 206 ...
250 207
251 The SPI device drivers only need to add ACPI I 208 The SPI device drivers only need to add ACPI IDs in a similar way to
252 the platform device drivers. Below is an examp 209 the platform device drivers. Below is an example where we add ACPI support
253 to at25 SPI eeprom driver (this is meant for t 210 to at25 SPI eeprom driver (this is meant for the above ACPI snippet)::
254 211
255 static const struct acpi_device_id at2 212 static const struct acpi_device_id at25_acpi_match[] = {
256 { "AT25", 0 }, 213 { "AT25", 0 },
257 { } 214 { }
258 }; 215 };
259 MODULE_DEVICE_TABLE(acpi, at25_acpi_ma 216 MODULE_DEVICE_TABLE(acpi, at25_acpi_match);
260 217
261 static struct spi_driver at25_driver = 218 static struct spi_driver at25_driver = {
262 .driver = { 219 .driver = {
263 ... 220 ...
264 .acpi_match_table = at 221 .acpi_match_table = at25_acpi_match,
265 }, 222 },
266 }; 223 };
267 224
268 Note that this driver actually needs more info 225 Note that this driver actually needs more information like page size of the
269 eeprom, etc. This information can be passed vi 226 eeprom, etc. This information can be passed via _DSD method like::
270 227
271 Device (EEP0) 228 Device (EEP0)
272 { 229 {
273 ... 230 ...
274 Name (_DSD, Package () 231 Name (_DSD, Package ()
275 { 232 {
276 ToUUID("daffd814-6eba- 233 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
277 Package () 234 Package ()
278 { 235 {
279 Package () { " 236 Package () { "size", 1024 },
280 Package () { " 237 Package () { "pagesize", 32 },
281 Package () { " 238 Package () { "address-width", 16 },
282 } 239 }
283 }) 240 })
284 } 241 }
285 242
286 Then the at25 SPI driver can get this configur 243 Then the at25 SPI driver can get this configuration by calling device property
287 APIs during ->probe() phase like:: 244 APIs during ->probe() phase like::
288 245
289 err = device_property_read_u32(dev, "s 246 err = device_property_read_u32(dev, "size", &size);
290 if (err) 247 if (err)
291 ...error handling... 248 ...error handling...
292 249
293 err = device_property_read_u32(dev, "p 250 err = device_property_read_u32(dev, "pagesize", &page_size);
294 if (err) 251 if (err)
295 ...error handling... 252 ...error handling...
296 253
297 err = device_property_read_u32(dev, "a 254 err = device_property_read_u32(dev, "address-width", &addr_width);
298 if (err) 255 if (err)
299 ...error handling... 256 ...error handling...
300 257
301 I2C serial bus support 258 I2C serial bus support
302 ====================== 259 ======================
303 260
304 The slaves behind I2C bus controller only need 261 The slaves behind I2C bus controller only need to add the ACPI IDs like
305 with the platform and SPI drivers. The I2C cor 262 with the platform and SPI drivers. The I2C core automatically enumerates
306 any slave devices behind the controller device 263 any slave devices behind the controller device once the adapter is
307 registered. 264 registered.
308 265
309 Below is an example of how to add ACPI support 266 Below is an example of how to add ACPI support to the existing mpu3050
310 input driver:: 267 input driver::
311 268
312 static const struct acpi_device_id mpu 269 static const struct acpi_device_id mpu3050_acpi_match[] = {
313 { "MPU3050", 0 }, 270 { "MPU3050", 0 },
314 { } 271 { }
315 }; 272 };
316 MODULE_DEVICE_TABLE(acpi, mpu3050_acpi 273 MODULE_DEVICE_TABLE(acpi, mpu3050_acpi_match);
317 274
318 static struct i2c_driver mpu3050_i2c_d 275 static struct i2c_driver mpu3050_i2c_driver = {
319 .driver = { 276 .driver = {
320 .name = "mpu3050", 277 .name = "mpu3050",
321 .pm = &mpu3050_pm, 278 .pm = &mpu3050_pm,
322 .of_match_table = mpu3 279 .of_match_table = mpu3050_of_match,
323 .acpi_match_table = mp 280 .acpi_match_table = mpu3050_acpi_match,
324 }, 281 },
325 .probe = mpu3050_prob 282 .probe = mpu3050_probe,
326 .remove = mpu3050_remo 283 .remove = mpu3050_remove,
327 .id_table = mpu3050_ids, 284 .id_table = mpu3050_ids,
328 }; 285 };
329 module_i2c_driver(mpu3050_i2c_driver); 286 module_i2c_driver(mpu3050_i2c_driver);
330 287
331 Reference to PWM device 288 Reference to PWM device
332 ======================= 289 =======================
333 290
334 Sometimes a device can be a consumer of PWM ch 291 Sometimes a device can be a consumer of PWM channel. Obviously OS would like
335 to know which one. To provide this mapping the 292 to know which one. To provide this mapping the special property has been
336 introduced, i.e.:: 293 introduced, i.e.::
337 294
338 Device (DEV) 295 Device (DEV)
339 { 296 {
340 Name (_DSD, Package () 297 Name (_DSD, Package ()
341 { 298 {
342 ToUUID("daffd814-6eba-4d8c-8a91-bc 299 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
343 Package () { 300 Package () {
344 Package () { "compatible", Pac 301 Package () { "compatible", Package () { "pwm-leds" } },
345 Package () { "label", "alarm-l 302 Package () { "label", "alarm-led" },
346 Package () { "pwms", 303 Package () { "pwms",
347 Package () { 304 Package () {
348 "\\_SB.PCI0.PWM", // 305 "\\_SB.PCI0.PWM", // <PWM device reference>
349 0, // 306 0, // <PWM index>
350 600000000, // 307 600000000, // <PWM period>
351 0, // 308 0, // <PWM flags>
352 } 309 }
353 } 310 }
354 } 311 }
355 }) 312 })
356 ... 313 ...
357 } 314 }
358 315
359 In the above example the PWM-based LED driver 316 In the above example the PWM-based LED driver references to the PWM channel 0
360 of \_SB.PCI0.PWM device with initial period se 317 of \_SB.PCI0.PWM device with initial period setting equal to 600 ms (note that
361 value is given in nanoseconds). 318 value is given in nanoseconds).
362 319
363 GPIO support 320 GPIO support
364 ============ 321 ============
365 322
366 ACPI 5 introduced two new resources to describ 323 ACPI 5 introduced two new resources to describe GPIO connections: GpioIo
367 and GpioInt. These resources can be used to pa 324 and GpioInt. These resources can be used to pass GPIO numbers used by
368 the device to the driver. ACPI 5.1 extended th 325 the device to the driver. ACPI 5.1 extended this with _DSD (Device
369 Specific Data) which made it possible to name 326 Specific Data) which made it possible to name the GPIOs among other things.
370 327
371 For example:: 328 For example::
372 329
373 Device (DEV) 330 Device (DEV)
374 { 331 {
375 Method (_CRS, 0, NotSerialized 332 Method (_CRS, 0, NotSerialized)
376 { 333 {
377 Name (SBUF, ResourceTe 334 Name (SBUF, ResourceTemplate()
378 { 335 {
379 // Used to pow 336 // Used to power on/off the device
380 GpioIo (Exclus 337 GpioIo (Exclusive, PullNone, 0, 0, IoRestrictionOutputOnly,
381 "\\_SB 338 "\\_SB.PCI0.GPI0", 0, ResourceConsumer) { 85 }
382 339
383 // Interrupt f 340 // Interrupt for the device
384 GpioInt (Edge, 341 GpioInt (Edge, ActiveHigh, ExclusiveAndWake, PullNone, 0,
385 "\\_S 342 "\\_SB.PCI0.GPI0", 0, ResourceConsumer) { 88 }
386 } 343 }
387 344
388 Return (SBUF) 345 Return (SBUF)
389 } 346 }
390 347
391 // ACPI 5.1 _DSD used for nami 348 // ACPI 5.1 _DSD used for naming the GPIOs
392 Name (_DSD, Package () 349 Name (_DSD, Package ()
393 { 350 {
394 ToUUID("daffd814-6eba- 351 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
395 Package () 352 Package ()
396 { 353 {
397 Package () { " 354 Package () { "power-gpios", Package () { ^DEV, 0, 0, 0 } },
398 Package () { " 355 Package () { "irq-gpios", Package () { ^DEV, 1, 0, 0 } },
399 } 356 }
400 }) 357 })
401 ... 358 ...
402 } 359 }
403 360
404 These GPIO numbers are controller relative and 361 These GPIO numbers are controller relative and path "\\_SB.PCI0.GPI0"
405 specifies the path to the controller. In order 362 specifies the path to the controller. In order to use these GPIOs in Linux
406 we need to translate them to the corresponding 363 we need to translate them to the corresponding Linux GPIO descriptors.
407 364
408 There is a standard GPIO API for that and it i 365 There is a standard GPIO API for that and it is documented in
409 Documentation/admin-guide/gpio/. 366 Documentation/admin-guide/gpio/.
410 367
411 In the above example we can get the correspond 368 In the above example we can get the corresponding two GPIO descriptors with
412 a code like this:: 369 a code like this::
413 370
414 #include <linux/gpio/consumer.h> 371 #include <linux/gpio/consumer.h>
415 ... 372 ...
416 373
417 struct gpio_desc *irq_desc, *power_des 374 struct gpio_desc *irq_desc, *power_desc;
418 375
419 irq_desc = gpiod_get(dev, "irq"); 376 irq_desc = gpiod_get(dev, "irq");
420 if (IS_ERR(irq_desc)) 377 if (IS_ERR(irq_desc))
421 /* handle error */ 378 /* handle error */
422 379
423 power_desc = gpiod_get(dev, "power"); 380 power_desc = gpiod_get(dev, "power");
424 if (IS_ERR(power_desc)) 381 if (IS_ERR(power_desc))
425 /* handle error */ 382 /* handle error */
426 383
427 /* Now we can use the GPIO descriptors 384 /* Now we can use the GPIO descriptors */
428 385
429 There are also devm_* versions of these functi 386 There are also devm_* versions of these functions which release the
430 descriptors once the device is released. 387 descriptors once the device is released.
431 388
432 See Documentation/firmware-guide/acpi/gpio-pro 389 See Documentation/firmware-guide/acpi/gpio-properties.rst for more information
433 about the _DSD binding related to GPIOs. 390 about the _DSD binding related to GPIOs.
434 391
435 RS-485 support 392 RS-485 support
436 ============== 393 ==============
437 394
438 ACPI _DSD (Device Specific Data) can be used t 395 ACPI _DSD (Device Specific Data) can be used to describe RS-485 capability
439 of UART. 396 of UART.
440 397
441 For example:: 398 For example::
442 399
443 Device (DEV) 400 Device (DEV)
444 { 401 {
445 ... 402 ...
446 403
447 // ACPI 5.1 _DSD used for RS-4 404 // ACPI 5.1 _DSD used for RS-485 capabilities
448 Name (_DSD, Package () 405 Name (_DSD, Package ()
449 { 406 {
450 ToUUID("daffd814-6eba- 407 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
451 Package () 408 Package ()
452 { 409 {
453 Package () {"r 410 Package () {"rs485-rts-active-low", Zero},
454 Package () {"r 411 Package () {"rs485-rx-active-high", Zero},
455 Package () {"r 412 Package () {"rs485-rx-during-tx", Zero},
456 } 413 }
457 }) 414 })
458 ... 415 ...
459 416
460 MFD devices 417 MFD devices
461 =========== 418 ===========
462 419
463 The MFD devices register their children as pla 420 The MFD devices register their children as platform devices. For the child
464 devices there needs to be an ACPI handle that 421 devices there needs to be an ACPI handle that they can use to reference
465 parts of the ACPI namespace that relate to the 422 parts of the ACPI namespace that relate to them. In the Linux MFD subsystem
466 we provide two ways: 423 we provide two ways:
467 424
468 - The children share the parent ACPI handle. 425 - The children share the parent ACPI handle.
469 - The MFD cell can specify the ACPI id of th 426 - The MFD cell can specify the ACPI id of the device.
470 427
471 For the first case, the MFD drivers do not nee 428 For the first case, the MFD drivers do not need to do anything. The
472 resulting child platform device will have its 429 resulting child platform device will have its ACPI_COMPANION() set to point
473 to the parent device. 430 to the parent device.
474 431
475 If the ACPI namespace has a device that we can 432 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:: 433 adr, the cell should be set like::
477 434
478 static struct mfd_cell_acpi_match my_s 435 static struct mfd_cell_acpi_match my_subdevice_cell_acpi_match = {
479 .pnpid = "XYZ0001", 436 .pnpid = "XYZ0001",
480 .adr = 0, 437 .adr = 0,
481 }; 438 };
482 439
483 static struct mfd_cell my_subdevice_ce 440 static struct mfd_cell my_subdevice_cell = {
484 .name = "my_subdevice", 441 .name = "my_subdevice",
485 /* set the resources relative 442 /* set the resources relative to the parent */
486 .acpi_match = &my_subdevice_ce 443 .acpi_match = &my_subdevice_cell_acpi_match,
487 }; 444 };
488 445
489 The ACPI id "XYZ0001" is then used to lookup a 446 The ACPI id "XYZ0001" is then used to lookup an ACPI device directly under
490 the MFD device and if found, that ACPI compani 447 the MFD device and if found, that ACPI companion device is bound to the
491 resulting child platform device. 448 resulting child platform device.
492 449
493 Device Tree namespace link device ID 450 Device Tree namespace link device ID
494 ==================================== 451 ====================================
495 452
496 The Device Tree protocol uses device identific 453 The Device Tree protocol uses device identification based on the "compatible"
497 property whose value is a string or an array o 454 property whose value is a string or an array of strings recognized as device
498 identifiers by drivers and the driver core. T 455 identifiers by drivers and the driver core. The set of all those strings may be
499 regarded as a device identification namespace 456 regarded as a device identification namespace analogous to the ACPI/PNP device
500 ID namespace. Consequently, in principle it s 457 ID namespace. Consequently, in principle it should not be necessary to allocate
501 a new (and arguably redundant) ACPI/PNP device 458 a new (and arguably redundant) ACPI/PNP device ID for a devices with an existing
502 identification string in the Device Tree (DT) 459 identification string in the Device Tree (DT) namespace, especially if that ID
503 is only needed to indicate that a given device 460 is only needed to indicate that a given device is compatible with another one,
504 presumably having a matching driver in the ker 461 presumably having a matching driver in the kernel already.
505 462
506 In ACPI, the device identification object call 463 In ACPI, the device identification object called _CID (Compatible ID) is used to
507 list the IDs of devices the given one is compa 464 list the IDs of devices the given one is compatible with, but those IDs must
508 belong to one of the namespaces prescribed by 465 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 466 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 467 Moreover, the specification mandates that either a _HID or an _ADR identification
511 object be present for all ACPI objects represe 468 object be present for all ACPI objects representing devices (Section 6.1 of ACPI
512 6.0). For non-enumerable bus types that objec 469 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 470 be a device ID from one of the namespaces prescribed by the specification too.
514 471
515 The special DT namespace link device ID, PRP00 472 The special DT namespace link device ID, PRP0001, provides a means to use the
516 existing DT-compatible device identification i 473 existing DT-compatible device identification in ACPI and to satisfy the above
517 requirements following from the ACPI specifica 474 requirements following from the ACPI specification at the same time. Namely,
518 if PRP0001 is returned by _HID, the ACPI subsy 475 if PRP0001 is returned by _HID, the ACPI subsystem will look for the
519 "compatible" property in the device object's _ 476 "compatible" property in the device object's _DSD and will use the value of that
520 property to identify the corresponding device 477 property to identify the corresponding device in analogy with the original DT
521 device identification algorithm. If the "comp 478 device identification algorithm. If the "compatible" property is not present
522 or its value is not valid, the device will not 479 or its value is not valid, the device will not be enumerated by the ACPI
523 subsystem. Otherwise, it will be enumerated a 480 subsystem. Otherwise, it will be enumerated automatically as a platform device
524 (except when an I2C or SPI link from the devic 481 (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 482 which case the ACPI core will leave the device enumeration to the parent's
526 driver) and the identification strings from th 483 driver) and the identification strings from the "compatible" property value will
527 be used to find a driver for the device along 484 be used to find a driver for the device along with the device IDs listed by _CID
528 (if present). 485 (if present).
529 486
530 Analogously, if PRP0001 is present in the list 487 Analogously, if PRP0001 is present in the list of device IDs returned by _CID,
531 the identification strings listed by the "comp 488 the identification strings listed by the "compatible" property value (if present
532 and valid) will be used to look for a driver m 489 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 490 case their relative priority with respect to the other device IDs listed by
534 _HID and _CID depends on the position of PRP00 491 _HID and _CID depends on the position of PRP0001 in the _CID return package.
535 Specifically, the device IDs returned by _HID 492 Specifically, the device IDs returned by _HID and preceding PRP0001 in the _CID
536 return package will be checked first. Also in 493 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 494 will be enumerated to depends on the device ID returned by _HID.
538 495
539 For example, the following ACPI sample might b 496 For example, the following ACPI sample might be used to enumerate an lm75-type
540 I2C temperature sensor and match it to the dri 497 I2C temperature sensor and match it to the driver using the Device Tree
541 namespace link:: 498 namespace link::
542 499
543 Device (TMP0) 500 Device (TMP0)
544 { 501 {
545 Name (_HID, "PRP0001") 502 Name (_HID, "PRP0001")
546 Name (_DSD, Package () { 503 Name (_DSD, Package () {
547 ToUUID("daffd814-6eba- 504 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
548 Package () { 505 Package () {
549 Package () { " 506 Package () { "compatible", "ti,tmp75" },
550 } 507 }
551 }) 508 })
552 Method (_CRS, 0, Serialized) 509 Method (_CRS, 0, Serialized)
553 { 510 {
554 Name (SBUF, ResourceTe 511 Name (SBUF, ResourceTemplate ()
555 { 512 {
556 I2cSerialBusV2 513 I2cSerialBusV2 (0x48, ControllerInitiated,
557 400000 514 400000, AddressingMode7Bit,
558 "\\_SB 515 "\\_SB.PCI0.I2C1", 0x00,
559 Resour 516 ResourceConsumer, , Exclusive,)
560 }) 517 })
561 Return (SBUF) 518 Return (SBUF)
562 } 519 }
563 } 520 }
564 521
565 It is valid to define device objects with a _H 522 It is valid to define device objects with a _HID returning PRP0001 and without
566 the "compatible" property in the _DSD or a _CI 523 the "compatible" property in the _DSD or a _CID as long as one of their
567 ancestors provides a _DSD with a valid "compat 524 ancestors provides a _DSD with a valid "compatible" property. Such device
568 objects are then simply regarded as additional 525 objects are then simply regarded as additional "blocks" providing hierarchical
569 configuration information to the driver of the 526 configuration information to the driver of the composite ancestor device.
570 527
571 However, PRP0001 can only be returned from eit 528 However, PRP0001 can only be returned from either _HID or _CID of a device
572 object if all of the properties returned by th 529 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 530 the _DSD of the device object itself or the _DSD of its ancestor in the
574 "composite device" case described above) can b 531 "composite device" case described above) can be used in the ACPI environment.
575 Otherwise, the _DSD itself is regarded as inva 532 Otherwise, the _DSD itself is regarded as invalid and therefore the "compatible"
576 property returned by it is meaningless. 533 property returned by it is meaningless.
577 534
578 Refer to Documentation/firmware-guide/acpi/DSD 535 Refer to Documentation/firmware-guide/acpi/DSD-properties-rules.rst for more
579 information. 536 information.
580 537
581 PCI hierarchy representation 538 PCI hierarchy representation
582 ============================ 539 ============================
583 540
584 Sometimes it could be useful to enumerate a PC 541 Sometimes it could be useful to enumerate a PCI device, knowing its position on
585 the PCI bus. 542 the PCI bus.
586 543
587 For example, some systems use PCI devices sold 544 For example, some systems use PCI devices soldered directly on the mother board,
588 in a fixed position (ethernet, Wi-Fi, serial p 545 in a fixed position (ethernet, Wi-Fi, serial ports, etc.). In this conditions it
589 is possible to refer to these PCI devices know 546 is possible to refer to these PCI devices knowing their position on the PCI bus
590 topology. 547 topology.
591 548
592 To identify a PCI device, a complete hierarchi 549 To identify a PCI device, a complete hierarchical description is required, from
593 the chipset root port to the final device, thr 550 the chipset root port to the final device, through all the intermediate
594 bridges/switches of the board. 551 bridges/switches of the board.
595 552
596 For example, let's assume we have a system wit 553 For example, let's assume we have a system with a PCIe serial port, an
597 Exar XR17V3521, soldered on the main board. Th 554 Exar XR17V3521, soldered on the main board. This UART chip also includes
598 16 GPIOs and we want to add the property ``gpi !! 555 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 556 In this case, the ``lspci`` output for this component is::
600 557
601 07:00.0 Serial controller: Exar Corp. 558 07:00.0 Serial controller: Exar Corp. XR17V3521 Dual PCIe UART (rev 03)
602 559
603 The complete ``lspci`` output (manually reduce 560 The complete ``lspci`` output (manually reduced in length) is::
604 561
605 00:00.0 Host bridge: Intel Corp... Hos 562 00:00.0 Host bridge: Intel Corp... Host Bridge (rev 0d)
606 ... 563 ...
607 00:13.0 PCI bridge: Intel Corp... PCI 564 00:13.0 PCI bridge: Intel Corp... PCI Express Port A #1 (rev fd)
608 00:13.1 PCI bridge: Intel Corp... PCI 565 00:13.1 PCI bridge: Intel Corp... PCI Express Port A #2 (rev fd)
609 00:13.2 PCI bridge: Intel Corp... PCI 566 00:13.2 PCI bridge: Intel Corp... PCI Express Port A #3 (rev fd)
610 00:14.0 PCI bridge: Intel Corp... PCI 567 00:14.0 PCI bridge: Intel Corp... PCI Express Port B #1 (rev fd)
611 00:14.1 PCI bridge: Intel Corp... PCI 568 00:14.1 PCI bridge: Intel Corp... PCI Express Port B #2 (rev fd)
612 ... 569 ...
613 05:00.0 PCI bridge: Pericom Semiconduc 570 05:00.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
614 06:01.0 PCI bridge: Pericom Semiconduc 571 06:01.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
615 06:02.0 PCI bridge: Pericom Semiconduc 572 06:02.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
616 06:03.0 PCI bridge: Pericom Semiconduc 573 06:03.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
617 07:00.0 Serial controller: Exar Corp. 574 07:00.0 Serial controller: Exar Corp. XR17V3521 Dual PCIe UART (rev 03) <-- Exar
618 ... 575 ...
619 576
620 The bus topology is:: 577 The bus topology is::
621 578
622 -[0000:00]-+-00.0 579 -[0000:00]-+-00.0
623 ... 580 ...
624 +-13.0-[01]----00.0 581 +-13.0-[01]----00.0
625 +-13.1-[02]----00.0 582 +-13.1-[02]----00.0
626 +-13.2-[03]-- 583 +-13.2-[03]--
627 +-14.0-[04]----00.0 584 +-14.0-[04]----00.0
628 +-14.1-[05-09]----00.0-[06- 585 +-14.1-[05-09]----00.0-[06-09]--+-01.0-[07]----00.0 <-- Exar
629 | 586 | +-02.0-[08]----00.0
630 | 587 | \-03.0-[09]--
631 ... 588 ...
632 \-1f.1 589 \-1f.1
633 590
634 To describe this Exar device on the PCI bus, w 591 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" 592 of the chipset bridge (also called "root port") with address::
636 593
637 Bus: 0 - Device: 14 - Function: 1 594 Bus: 0 - Device: 14 - Function: 1
638 595
639 To find this information, it is necessary to d 596 To find this information, it is necessary to disassemble the BIOS ACPI tables,
640 in particular the DSDT (see also [2]_):: !! 597 in particular the DSDT (see also [2])::
641 598
642 mkdir ~/tables/ 599 mkdir ~/tables/
643 cd ~/tables/ 600 cd ~/tables/
644 acpidump > acpidump 601 acpidump > acpidump
645 acpixtract -a acpidump 602 acpixtract -a acpidump
646 iasl -e ssdt?.* -d dsdt.dat 603 iasl -e ssdt?.* -d dsdt.dat
647 604
648 Now, in the dsdt.dsl, we have to search the de 605 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 606 0x14 (device) and 0x01 (function). In this case we can find the following
650 device:: 607 device::
651 608
652 Scope (_SB.PCI0) 609 Scope (_SB.PCI0)
653 { 610 {
654 ... other definitions follow ... 611 ... other definitions follow ...
655 Device (RP02) 612 Device (RP02)
656 { 613 {
657 Method (_ADR, 0, NotSe 614 Method (_ADR, 0, NotSerialized) // _ADR: Address
658 { 615 {
659 If ((RPA2 != Z 616 If ((RPA2 != Zero))
660 { 617 {
661 Return 618 Return (RPA2) /* \RPA2 */
662 } 619 }
663 Else 620 Else
664 { 621 {
665 Return 622 Return (0x00140001)
666 } 623 }
667 } 624 }
668 ... other definitions follow ... 625 ... other definitions follow ...
669 626
670 and the _ADR method [3]_ returns exactly the d !! 627 and the _ADR method [3] returns exactly the device/function couple that
671 we are looking for. With this information and 628 we are looking for. With this information and analyzing the above ``lspci``
672 output (both the devices list and the devices 629 output (both the devices list and the devices tree), we can write the following
673 ACPI description for the Exar PCIe UART, also 630 ACPI description for the Exar PCIe UART, also adding the list of its GPIO line
674 names:: 631 names::
675 632
676 Scope (_SB.PCI0.RP02) 633 Scope (_SB.PCI0.RP02)
677 { 634 {
678 Device (BRG1) //Bridge 635 Device (BRG1) //Bridge
679 { 636 {
680 Name (_ADR, 0x0000) 637 Name (_ADR, 0x0000)
681 638
682 Device (BRG2) //Bridge 639 Device (BRG2) //Bridge
683 { 640 {
684 Name (_ADR, 0x 641 Name (_ADR, 0x00010000)
685 642
686 Device (EXAR) 643 Device (EXAR)
687 { 644 {
688 Name ( 645 Name (_ADR, 0x0000)
689 646
690 Name ( 647 Name (_DSD, Package ()
691 { 648 {
692 649 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
693 650 Package ()
694 651 {
695 652 Package ()
696 653 {
697 654 "gpio-line-names",
698 655 Package ()
699 656 {
700 657 "mode_232",
701 658 "mode_422",
702 659 "mode_485",
703 660 "misc_1",
704 661 "misc_2",
705 662 "misc_3",
706 663 "",
707 664 "",
708 665 "aux_1",
709 666 "aux_2",
710 667 "aux_3",
711 668 }
712 669 }
713 670 }
714 }) 671 })
715 } 672 }
716 } 673 }
717 } 674 }
718 } 675 }
719 676
720 The location "_SB.PCI0.RP02" is obtained by th 677 The location "_SB.PCI0.RP02" is obtained by the above investigation in the
721 dsdt.dsl table, whereas the device names "BRG1 678 dsdt.dsl table, whereas the device names "BRG1", "BRG2" and "EXAR" are
722 created analyzing the position of the Exar UAR 679 created analyzing the position of the Exar UART in the PCI bus topology.
723 680
724 References 681 References
725 ========== 682 ==========
726 683
727 .. [1] Documentation/firmware-guide/acpi/gpio- !! 684 [1] Documentation/firmware-guide/acpi/gpio-properties.rst
728 685
729 .. [2] Documentation/admin-guide/acpi/initrd_t !! 686 [2] Documentation/admin-guide/acpi/initrd_table_override.rst
730 687
731 .. [3] ACPI Specifications, Version 6.3 - Para !! 688 [3] ACPI Specifications, Version 6.3 - Paragraph 6.1.1 _ADR Address)
732 https://uefi.org/sites/default/files/resou 689 https://uefi.org/sites/default/files/resources/ACPI_6_3_May16.pdf,
733 referenced 2020-11-18 690 referenced 2020-11-18
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