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