1 .. SPDX-License-Identifier: GPL-2.0
2
3 =============================
4 ACPI Based Device Enumeration
5 =============================
6
7 ACPI 5 introduced a set of new resources (UartTSerialBus, I2cSerialBus,
8 SpiSerialBus, GpioIo and GpioInt) which can be used in enumerating slave
9 devices behind serial bus controllers.
10
11 In addition we are starting to see peripherals integrated in the
12 SoC/Chipset to appear only in ACPI namespace. These are typically devices
13 that are accessed through memory-mapped registers.
14
15 In order to support this and re-use the existing drivers as much as
16 possible we decided to do following:
17
18 - Devices that have no bus connector resource are represented as
19 platform devices.
20
21 - Devices behind real busses where there is a connector resource
22 are represented as struct spi_device or struct i2c_client. Note
23 that standard UARTs are not busses so there is no struct uart_device,
24 although some of them may be represented by struct serdev_device.
25
26 As both ACPI and Device Tree represent a tree of devices (and their
27 resources) this implementation follows the Device Tree way as much as
28 possible.
29
30 The ACPI implementation enumerates devices behind busses (platform, SPI,
31 I2C, and in some cases UART), creates the physical devices and binds them
32 to their ACPI handle in the ACPI namespace.
33
34 This means that when ACPI_HANDLE(dev) returns non-NULL the device was
35 enumerated from ACPI namespace. This handle can be used to extract other
36 device-specific configuration. There is an example of this below.
37
38 Platform bus support
39 ====================
40
41 Since we are using platform devices to represent devices that are not
42 connected to any physical bus we only need to implement a platform driver
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 work out of the box or needs
45 some minor changes.
46
47 Adding ACPI support for an existing driver should be pretty
48 straightforward. Here is the simplest example::
49
50 static const struct acpi_device_id mydrv_acpi_match[] = {
51 /* ACPI IDs here */
52 { }
53 };
54 MODULE_DEVICE_TABLE(acpi, mydrv_acpi_match);
55
56 static struct platform_driver my_driver = {
57 ...
58 .driver = {
59 .acpi_match_table = mydrv_acpi_match,
60 },
61 };
62
63 If the driver needs to perform more complex initialization like getting and
64 configuring GPIOs it can get its ACPI handle and extract this information
65 from ACPI tables.
66
67 ACPI device objects
68 ===================
69
70 Generally speaking, there are two categories of devices in a system in which
71 ACPI is used as an interface between the platform firmware and the OS: Devices
72 that can be discovered and enumerated natively, through a protocol defined for
73 the specific bus that they are on (for example, configuration space in PCI),
74 without the platform firmware assistance, and devices that need to be described
75 by the platform firmware so that they can be discovered. Still, for any device
76 known to the platform firmware, regardless of which category it falls into,
77 there can be a corresponding ACPI device object in the ACPI Namespace in which
78 case the Linux kernel will create a struct acpi_device object based on it for
79 that device.
80
81 Those struct acpi_device objects are never used for binding drivers to natively
82 discoverable devices, because they are represented by other types of device
83 objects (for example, struct pci_dev for PCI devices) that are bound to by
84 device drivers (the corresponding struct acpi_device object is then used as
85 an additional source of information on the configuration of the given device).
86 Moreover, the core ACPI device enumeration code creates struct platform_device
87 objects for the majority of devices that are discovered and enumerated with the
88 help of the platform firmware and those platform device objects can be bound to
89 by platform drivers in direct analogy with the natively enumerable devices
90 case. Therefore it is logically inconsistent and so generally invalid to bind
91 drivers to struct acpi_device objects, including drivers for devices that are
92 discovered with the help of the platform firmware.
93
94 Historically, ACPI drivers that bound directly to struct acpi_device objects
95 were implemented for some devices enumerated with the help of the platform
96 firmware, but this is not recommended for any new drivers. As explained above,
97 platform device objects are created for those devices as a rule (with a few
98 exceptions that are not relevant here) and so platform drivers should be used
99 for handling them, even though the corresponding ACPI device objects are the
100 only source of device configuration information in that case.
101
102 For every device having a corresponding struct acpi_device object, the pointer
103 to it is returned by the ACPI_COMPANION() macro, so it is always possible to
104 get to the device configuration information stored in the ACPI device object
105 this way. Accordingly, struct acpi_device can be regarded as a part of the
106 interface between the kernel and the ACPI Namespace, whereas device objects of
107 other types (for example, struct pci_dev or struct platform_device) are used
108 for interacting with the rest of the system.
109
110 DMA support
111 ===========
112
113 DMA controllers enumerated via ACPI should be registered in the system to
114 provide generic access to their resources. For example, a driver that would
115 like to be accessible to slave devices via generic API call
116 dma_request_chan() must register itself at the end of the probe function like
117 this::
118
119 err = devm_acpi_dma_controller_register(dev, xlate_func, dw);
120 /* Handle the error if it's not a case of !CONFIG_ACPI */
121
122 and implement custom xlate function if needed (usually acpi_dma_simple_xlate()
123 is enough) which converts the FixedDMA resource provided by struct
124 acpi_dma_spec into the corresponding DMA channel. A piece of code for that case
125 could look like::
126
127 #ifdef CONFIG_ACPI
128 struct filter_args {
129 /* Provide necessary information for the filter_func */
130 ...
131 };
132
133 static bool filter_func(struct dma_chan *chan, void *param)
134 {
135 /* Choose the proper channel */
136 ...
137 }
138
139 static struct dma_chan *xlate_func(struct acpi_dma_spec *dma_spec,
140 struct acpi_dma *adma)
141 {
142 dma_cap_mask_t cap;
143 struct filter_args args;
144
145 /* Prepare arguments for filter_func */
146 ...
147 return dma_request_channel(cap, filter_func, &args);
148 }
149 #else
150 static struct dma_chan *xlate_func(struct acpi_dma_spec *dma_spec,
151 struct acpi_dma *adma)
152 {
153 return NULL;
154 }
155 #endif
156
157 dma_request_chan() will call xlate_func() for each registered DMA controller.
158 In the xlate function the proper channel must be chosen based on
159 information in struct acpi_dma_spec and the properties of the controller
160 provided by struct acpi_dma.
161
162 Clients must call dma_request_chan() with the string parameter that corresponds
163 to a specific FixedDMA resource. By default "tx" means the first entry of the
164 FixedDMA resource array, "rx" means the second entry. The table below shows a
165 layout::
166
167 Device (I2C0)
168 {
169 ...
170 Method (_CRS, 0, NotSerialized)
171 {
172 Name (DBUF, ResourceTemplate ()
173 {
174 FixedDMA (0x0018, 0x0004, Width32bit, _Y48)
175 FixedDMA (0x0019, 0x0005, Width32bit, )
176 })
177 ...
178 }
179 }
180
181 So, the FixedDMA with request line 0x0018 is "tx" and next one is "rx" in
182 this example.
183
184 In robust cases the client unfortunately needs to call
185 acpi_dma_request_slave_chan_by_index() directly and therefore choose the
186 specific FixedDMA resource by its index.
187
188 Named Interrupts
189 ================
190
191 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 driver.
193
194 The interrupt name can be listed in _DSD as 'interrupt-names'. The names
195 should be listed as an array of strings which will map to the Interrupt()
196 resource in the ACPI table corresponding to its index.
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, ActiveHigh, Exclusive) {
205 0x20,
206 0x24
207 }
208 })
209
210 Name (_DSD, Package () {
211 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
212 Package () {
213 Package () { "interrupt-names", Package () { "default", "alert" } },
214 }
215 ...
216 })
217 }
218
219 The interrupt name 'default' will correspond to 0x20 in Interrupt()
220 resource and 'alert' to 0x24. Note that only the Interrupt() resource
221 is mapped and not GpioInt() or similar.
222
223 The driver can call the function - fwnode_irq_get_byname() with the fwnode
224 and interrupt name as arguments to get the corresponding IRQ number.
225
226 SPI serial bus support
227 ======================
228
229 Slave devices behind SPI bus have SpiSerialBus resource attached to them.
230 This is extracted automatically by the SPI core and the slave devices are
231 enumerated once spi_register_master() is called by the bus driver.
232
233 Here is what the ACPI namespace for a SPI slave might look like::
234
235 Device (EEP0)
236 {
237 Name (_ADR, 1)
238 Name (_CID, Package () {
239 "ATML0025",
240 "AT25",
241 })
242 ...
243 Method (_CRS, 0, NotSerialized)
244 {
245 SPISerialBus(1, PolarityLow, FourWireMode, 8,
246 ControllerInitiated, 1000000, ClockPolarityLow,
247 ClockPhaseFirst, "\\_SB.PCI0.SPI1",)
248 }
249 ...
250
251 The SPI device drivers only need to add ACPI IDs in a similar way to
252 the platform device drivers. Below is an example where we add ACPI support
253 to at25 SPI eeprom driver (this is meant for the above ACPI snippet)::
254
255 static const struct acpi_device_id at25_acpi_match[] = {
256 { "AT25", 0 },
257 { }
258 };
259 MODULE_DEVICE_TABLE(acpi, at25_acpi_match);
260
261 static struct spi_driver at25_driver = {
262 .driver = {
263 ...
264 .acpi_match_table = at25_acpi_match,
265 },
266 };
267
268 Note that this driver actually needs more information like page size of the
269 eeprom, etc. This information can be passed via _DSD method like::
270
271 Device (EEP0)
272 {
273 ...
274 Name (_DSD, Package ()
275 {
276 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
277 Package ()
278 {
279 Package () { "size", 1024 },
280 Package () { "pagesize", 32 },
281 Package () { "address-width", 16 },
282 }
283 })
284 }
285
286 Then the at25 SPI driver can get this configuration by calling device property
287 APIs during ->probe() phase like::
288
289 err = device_property_read_u32(dev, "size", &size);
290 if (err)
291 ...error handling...
292
293 err = device_property_read_u32(dev, "pagesize", &page_size);
294 if (err)
295 ...error handling...
296
297 err = device_property_read_u32(dev, "address-width", &addr_width);
298 if (err)
299 ...error handling...
300
301 I2C serial bus support
302 ======================
303
304 The slaves behind I2C bus controller only need to add the ACPI IDs like
305 with the platform and SPI drivers. The I2C core automatically enumerates
306 any slave devices behind the controller device once the adapter is
307 registered.
308
309 Below is an example of how to add ACPI support to the existing mpu3050
310 input driver::
311
312 static const struct acpi_device_id mpu3050_acpi_match[] = {
313 { "MPU3050", 0 },
314 { }
315 };
316 MODULE_DEVICE_TABLE(acpi, mpu3050_acpi_match);
317
318 static struct i2c_driver mpu3050_i2c_driver = {
319 .driver = {
320 .name = "mpu3050",
321 .pm = &mpu3050_pm,
322 .of_match_table = mpu3050_of_match,
323 .acpi_match_table = mpu3050_acpi_match,
324 },
325 .probe = mpu3050_probe,
326 .remove = mpu3050_remove,
327 .id_table = mpu3050_ids,
328 };
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 channel. Obviously OS would like
335 to know which one. To provide this mapping the special property has been
336 introduced, i.e.::
337
338 Device (DEV)
339 {
340 Name (_DSD, Package ()
341 {
342 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
343 Package () {
344 Package () { "compatible", Package () { "pwm-leds" } },
345 Package () { "label", "alarm-led" },
346 Package () { "pwms",
347 Package () {
348 "\\_SB.PCI0.PWM", // <PWM device reference>
349 0, // <PWM index>
350 600000000, // <PWM period>
351 0, // <PWM flags>
352 }
353 }
354 }
355 })
356 ...
357 }
358
359 In the above example the PWM-based LED driver references to the PWM channel 0
360 of \_SB.PCI0.PWM device with initial period setting equal to 600 ms (note that
361 value is given in nanoseconds).
362
363 GPIO support
364 ============
365
366 ACPI 5 introduced two new resources to describe GPIO connections: GpioIo
367 and GpioInt. These resources can be used to pass GPIO numbers used by
368 the device to the driver. ACPI 5.1 extended this with _DSD (Device
369 Specific Data) which made it possible to name the GPIOs among other things.
370
371 For example::
372
373 Device (DEV)
374 {
375 Method (_CRS, 0, NotSerialized)
376 {
377 Name (SBUF, ResourceTemplate()
378 {
379 // Used to power on/off the device
380 GpioIo (Exclusive, PullNone, 0, 0, IoRestrictionOutputOnly,
381 "\\_SB.PCI0.GPI0", 0, ResourceConsumer) { 85 }
382
383 // Interrupt for the device
384 GpioInt (Edge, ActiveHigh, ExclusiveAndWake, PullNone, 0,
385 "\\_SB.PCI0.GPI0", 0, ResourceConsumer) { 88 }
386 }
387
388 Return (SBUF)
389 }
390
391 // ACPI 5.1 _DSD used for naming the GPIOs
392 Name (_DSD, Package ()
393 {
394 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
395 Package ()
396 {
397 Package () { "power-gpios", Package () { ^DEV, 0, 0, 0 } },
398 Package () { "irq-gpios", Package () { ^DEV, 1, 0, 0 } },
399 }
400 })
401 ...
402 }
403
404 These GPIO numbers are controller relative and path "\\_SB.PCI0.GPI0"
405 specifies the path to the controller. In order to use these GPIOs in Linux
406 we need to translate them to the corresponding Linux GPIO descriptors.
407
408 There is a standard GPIO API for that and it is documented in
409 Documentation/admin-guide/gpio/.
410
411 In the above example we can get the corresponding two GPIO descriptors with
412 a code like this::
413
414 #include <linux/gpio/consumer.h>
415 ...
416
417 struct gpio_desc *irq_desc, *power_desc;
418
419 irq_desc = gpiod_get(dev, "irq");
420 if (IS_ERR(irq_desc))
421 /* handle error */
422
423 power_desc = gpiod_get(dev, "power");
424 if (IS_ERR(power_desc))
425 /* handle error */
426
427 /* Now we can use the GPIO descriptors */
428
429 There are also devm_* versions of these functions which release the
430 descriptors once the device is released.
431
432 See Documentation/firmware-guide/acpi/gpio-properties.rst for more information
433 about the _DSD binding related to GPIOs.
434
435 RS-485 support
436 ==============
437
438 ACPI _DSD (Device Specific Data) can be used to describe RS-485 capability
439 of UART.
440
441 For example::
442
443 Device (DEV)
444 {
445 ...
446
447 // ACPI 5.1 _DSD used for RS-485 capabilities
448 Name (_DSD, Package ()
449 {
450 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
451 Package ()
452 {
453 Package () {"rs485-rts-active-low", Zero},
454 Package () {"rs485-rx-active-high", Zero},
455 Package () {"rs485-rx-during-tx", Zero},
456 }
457 })
458 ...
459
460 MFD devices
461 ===========
462
463 The MFD devices register their children as platform devices. For the child
464 devices there needs to be an ACPI handle that they can use to reference
465 parts of the ACPI namespace that relate to them. In the Linux MFD subsystem
466 we provide two ways:
467
468 - The children share the parent ACPI handle.
469 - The MFD cell can specify the ACPI id of the device.
470
471 For the first case, the MFD drivers do not need to do anything. The
472 resulting child platform device will have its ACPI_COMPANION() set to point
473 to the parent device.
474
475 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::
477
478 static struct mfd_cell_acpi_match my_subdevice_cell_acpi_match = {
479 .pnpid = "XYZ0001",
480 .adr = 0,
481 };
482
483 static struct mfd_cell my_subdevice_cell = {
484 .name = "my_subdevice",
485 /* set the resources relative to the parent */
486 .acpi_match = &my_subdevice_cell_acpi_match,
487 };
488
489 The ACPI id "XYZ0001" is then used to lookup an ACPI device directly under
490 the MFD device and if found, that ACPI companion device is bound to the
491 resulting child platform device.
492
493 Device Tree namespace link device ID
494 ====================================
495
496 The Device Tree protocol uses device identification based on the "compatible"
497 property whose value is a string or an array of strings recognized as device
498 identifiers by drivers and the driver core. The set of all those strings may be
499 regarded as a device identification namespace analogous to the ACPI/PNP device
500 ID namespace. Consequently, in principle it should not be necessary to allocate
501 a new (and arguably redundant) ACPI/PNP device ID for a devices with an existing
502 identification string in the Device Tree (DT) namespace, especially if that ID
503 is only needed to indicate that a given device is compatible with another one,
504 presumably having a matching driver in the kernel already.
505
506 In ACPI, the device identification object called _CID (Compatible ID) is used to
507 list the IDs of devices the given one is compatible with, but those IDs must
508 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 DT namespace is not one of them.
510 Moreover, the specification mandates that either a _HID or an _ADR identification
511 object be present for all ACPI objects representing devices (Section 6.1 of ACPI
512 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 prescribed by the specification too.
514
515 The special DT namespace link device ID, PRP0001, provides a means to use the
516 existing DT-compatible device identification in ACPI and to satisfy the above
517 requirements following from the ACPI specification at the same time. Namely,
518 if PRP0001 is returned by _HID, the ACPI subsystem will look for the
519 "compatible" property in the device object's _DSD and will use the value of that
520 property to identify the corresponding device in analogy with the original DT
521 device identification algorithm. If the "compatible" property is not present
522 or its value is not valid, the device will not be enumerated by the ACPI
523 subsystem. Otherwise, it will be enumerated automatically as a platform device
524 (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 enumeration to the parent's
526 driver) and the identification strings from the "compatible" property value will
527 be used to find a driver for the device along with the device IDs listed by _CID
528 (if present).
529
530 Analogously, if PRP0001 is present in the list of device IDs returned by _CID,
531 the identification strings listed by the "compatible" property value (if present
532 and valid) will be used to look for a driver matching the device, but in that
533 case their relative priority with respect to the other device IDs listed by
534 _HID and _CID depends on the position of PRP0001 in the _CID return package.
535 Specifically, the device IDs returned by _HID and preceding PRP0001 in the _CID
536 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 returned by _HID.
538
539 For example, the following ACPI sample might be used to enumerate an lm75-type
540 I2C temperature sensor and match it to the driver using the Device Tree
541 namespace link::
542
543 Device (TMP0)
544 {
545 Name (_HID, "PRP0001")
546 Name (_DSD, Package () {
547 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
548 Package () {
549 Package () { "compatible", "ti,tmp75" },
550 }
551 })
552 Method (_CRS, 0, Serialized)
553 {
554 Name (SBUF, ResourceTemplate ()
555 {
556 I2cSerialBusV2 (0x48, ControllerInitiated,
557 400000, AddressingMode7Bit,
558 "\\_SB.PCI0.I2C1", 0x00,
559 ResourceConsumer, , Exclusive,)
560 })
561 Return (SBUF)
562 }
563 }
564
565 It is valid to define device objects with a _HID returning PRP0001 and without
566 the "compatible" property in the _DSD or a _CID as long as one of their
567 ancestors provides a _DSD with a valid "compatible" property. Such device
568 objects are then simply regarded as additional "blocks" providing hierarchical
569 configuration information to the driver of the composite ancestor device.
570
571 However, PRP0001 can only be returned from either _HID or _CID of a device
572 object if all of the properties returned by the _DSD associated with it (either
573 the _DSD of the device object itself or the _DSD of its ancestor in the
574 "composite device" case described above) can be used in the ACPI environment.
575 Otherwise, the _DSD itself is regarded as invalid and therefore the "compatible"
576 property returned by it is meaningless.
577
578 Refer to Documentation/firmware-guide/acpi/DSD-properties-rules.rst for more
579 information.
580
581 PCI hierarchy representation
582 ============================
583
584 Sometimes it could be useful to enumerate a PCI device, knowing its position on
585 the PCI bus.
586
587 For example, some systems use PCI devices soldered directly on the mother board,
588 in a fixed position (ethernet, Wi-Fi, serial ports, etc.). In this conditions it
589 is possible to refer to these PCI devices knowing their position on the PCI bus
590 topology.
591
592 To identify a PCI device, a complete hierarchical description is required, from
593 the chipset root port to the final device, through all the intermediate
594 bridges/switches of the board.
595
596 For example, let's assume we have a system with a PCIe serial port, an
597 Exar XR17V3521, soldered on the main board. This UART chip also includes
598 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 component is::
600
601 07:00.0 Serial controller: Exar Corp. XR17V3521 Dual PCIe UART (rev 03)
602
603 The complete ``lspci`` output (manually reduced in length) is::
604
605 00:00.0 Host bridge: Intel Corp... Host Bridge (rev 0d)
606 ...
607 00:13.0 PCI bridge: Intel Corp... PCI Express Port A #1 (rev fd)
608 00:13.1 PCI bridge: Intel Corp... PCI Express Port A #2 (rev fd)
609 00:13.2 PCI bridge: Intel Corp... PCI Express Port A #3 (rev fd)
610 00:14.0 PCI bridge: Intel Corp... PCI Express Port B #1 (rev fd)
611 00:14.1 PCI bridge: Intel Corp... PCI Express Port B #2 (rev fd)
612 ...
613 05:00.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
614 06:01.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
615 06:02.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
616 06:03.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
617 07:00.0 Serial controller: Exar Corp. XR17V3521 Dual PCIe UART (rev 03) <-- Exar
618 ...
619
620 The bus topology is::
621
622 -[0000:00]-+-00.0
623 ...
624 +-13.0-[01]----00.0
625 +-13.1-[02]----00.0
626 +-13.2-[03]--
627 +-14.0-[04]----00.0
628 +-14.1-[05-09]----00.0-[06-09]--+-01.0-[07]----00.0 <-- Exar
629 | +-02.0-[08]----00.0
630 | \-03.0-[09]--
631 ...
632 \-1f.1
633
634 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") with address::
636
637 Bus: 0 - Device: 14 - Function: 1
638
639 To find this information, it is necessary to disassemble the BIOS ACPI tables,
640 in particular the DSDT (see also [2]_)::
641
642 mkdir ~/tables/
643 cd ~/tables/
644 acpidump > acpidump
645 acpixtract -a acpidump
646 iasl -e ssdt?.* -d dsdt.dat
647
648 Now, in the dsdt.dsl, we have to search the device whose address is related to
649 0x14 (device) and 0x01 (function). In this case we can find the following
650 device::
651
652 Scope (_SB.PCI0)
653 {
654 ... other definitions follow ...
655 Device (RP02)
656 {
657 Method (_ADR, 0, NotSerialized) // _ADR: Address
658 {
659 If ((RPA2 != Zero))
660 {
661 Return (RPA2) /* \RPA2 */
662 }
663 Else
664 {
665 Return (0x00140001)
666 }
667 }
668 ... other definitions follow ...
669
670 and the _ADR method [3]_ returns exactly the device/function couple that
671 we are looking for. With this information and analyzing the above ``lspci``
672 output (both the devices list and the devices tree), we can write the following
673 ACPI description for the Exar PCIe UART, also adding the list of its GPIO line
674 names::
675
676 Scope (_SB.PCI0.RP02)
677 {
678 Device (BRG1) //Bridge
679 {
680 Name (_ADR, 0x0000)
681
682 Device (BRG2) //Bridge
683 {
684 Name (_ADR, 0x00010000)
685
686 Device (EXAR)
687 {
688 Name (_ADR, 0x0000)
689
690 Name (_DSD, Package ()
691 {
692 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
693 Package ()
694 {
695 Package ()
696 {
697 "gpio-line-names",
698 Package ()
699 {
700 "mode_232",
701 "mode_422",
702 "mode_485",
703 "misc_1",
704 "misc_2",
705 "misc_3",
706 "",
707 "",
708 "aux_1",
709 "aux_2",
710 "aux_3",
711 }
712 }
713 }
714 })
715 }
716 }
717 }
718 }
719
720 The location "_SB.PCI0.RP02" is obtained by the above investigation in the
721 dsdt.dsl table, whereas the device names "BRG1", "BRG2" and "EXAR" are
722 created analyzing the position of the Exar UART in the PCI bus topology.
723
724 References
725 ==========
726
727 .. [1] Documentation/firmware-guide/acpi/gpio-properties.rst
728
729 .. [2] Documentation/admin-guide/acpi/initrd_table_override.rst
730
731 .. [3] ACPI Specifications, Version 6.3 - Paragraph 6.1.1 _ADR Address)
732 https://uefi.org/sites/default/files/resources/ACPI_6_3_May16.pdf,
733 referenced 2020-11-18
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