1.. SPDX-License-Identifier: GPL-2.0
2
3=============================
4ACPI Based Device Enumeration
5=============================
6
7ACPI 5 introduced a set of new resources (UartTSerialBus, I2cSerialBus,
8SpiSerialBus, GpioIo and GpioInt) which can be used in enumerating slave
9devices behind serial bus controllers.
10
11In addition we are starting to see peripherals integrated in the
12SoC/Chipset to appear only in ACPI namespace. These are typically devices
13that are accessed through memory-mapped registers.
14
15In order to support this and re-use the existing drivers as much as
16possible 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_device. Note
23    that standard UARTs are not busses so there is no struct uart_device,
24    although some of them may be represented by sturct serdev_device.
25
26As both ACPI and Device Tree represent a tree of devices (and their
27resources) this implementation follows the Device Tree way as much as
28possible.
29
30The ACPI implementation enumerates devices behind busses (platform, SPI,
31I2C, and in some cases UART), creates the physical devices and binds them
32to their ACPI handle in the ACPI namespace.
33
34This means that when ACPI_HANDLE(dev) returns non-NULL the device was
35enumerated from ACPI namespace. This handle can be used to extract other
36device-specific configuration. There is an example of this below.
37
38Platform bus support
39====================
40
41Since we are using platform devices to represent devices that are not
42connected to any physical bus we only need to implement a platform driver
43for the device and add supported ACPI IDs. If this same IP-block is used on
44some other non-ACPI platform, the driver might work out of the box or needs
45some minor changes.
46
47Adding ACPI support for an existing driver should be pretty
48straightforward. 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
63If the driver needs to perform more complex initialization like getting and
64configuring GPIOs it can get its ACPI handle and extract this information
65from ACPI tables.
66
67DMA support
68===========
69
70DMA controllers enumerated via ACPI should be registered in the system to
71provide generic access to their resources. For example, a driver that would
72like to be accessible to slave devices via generic API call
73dma_request_chan() must register itself at the end of the probe function like
74this::
75
76	err = devm_acpi_dma_controller_register(dev, xlate_func, dw);
77	/* Handle the error if it's not a case of !CONFIG_ACPI */
78
79and implement custom xlate function if needed (usually acpi_dma_simple_xlate()
80is enough) which converts the FixedDMA resource provided by struct
81acpi_dma_spec into the corresponding DMA channel. A piece of code for that case
82could look like::
83
84	#ifdef CONFIG_ACPI
85	struct filter_args {
86		/* Provide necessary information for the filter_func */
87		...
88	};
89
90	static bool filter_func(struct dma_chan *chan, void *param)
91	{
92		/* Choose the proper channel */
93		...
94	}
95
96	static struct dma_chan *xlate_func(struct acpi_dma_spec *dma_spec,
97			struct acpi_dma *adma)
98	{
99		dma_cap_mask_t cap;
100		struct filter_args args;
101
102		/* Prepare arguments for filter_func */
103		...
104		return dma_request_channel(cap, filter_func, &args);
105	}
106	#else
107	static struct dma_chan *xlate_func(struct acpi_dma_spec *dma_spec,
108			struct acpi_dma *adma)
109	{
110		return NULL;
111	}
112	#endif
113
114dma_request_chan() will call xlate_func() for each registered DMA controller.
115In the xlate function the proper channel must be chosen based on
116information in struct acpi_dma_spec and the properties of the controller
117provided by struct acpi_dma.
118
119Clients must call dma_request_chan() with the string parameter that corresponds
120to a specific FixedDMA resource. By default "tx" means the first entry of the
121FixedDMA resource array, "rx" means the second entry. The table below shows a
122layout::
123
124	Device (I2C0)
125	{
126		...
127		Method (_CRS, 0, NotSerialized)
128		{
129			Name (DBUF, ResourceTemplate ()
130			{
131				FixedDMA (0x0018, 0x0004, Width32bit, _Y48)
132				FixedDMA (0x0019, 0x0005, Width32bit, )
133			})
134		...
135		}
136	}
137
138So, the FixedDMA with request line 0x0018 is "tx" and next one is "rx" in
139this example.
140
141In robust cases the client unfortunately needs to call
142acpi_dma_request_slave_chan_by_index() directly and therefore choose the
143specific FixedDMA resource by its index.
144
145Named Interrupts
146================
147
148Drivers enumerated via ACPI can have names to interrupts in the ACPI table
149which can be used to get the IRQ number in the driver.
150
151The interrupt name can be listed in _DSD as 'interrupt-names'. The names
152should be listed as an array of strings which will map to the Interrupt()
153resource in the ACPI table corresponding to its index.
154
155The table below shows an example of its usage::
156
157    Device (DEV0) {
158        ...
159        Name (_CRS, ResourceTemplate() {
160            ...
161            Interrupt (ResourceConsumer, Level, ActiveHigh, Exclusive) {
162                0x20,
163                0x24
164            }
165        })
166
167        Name (_DSD, Package () {
168            ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
169            Package () {
170                Package () { "interrupt-names", Package () { "default", "alert" } },
171            }
172        ...
173        })
174    }
175
176The interrupt name 'default' will correspond to 0x20 in Interrupt()
177resource and 'alert' to 0x24. Note that only the Interrupt() resource
178is mapped and not GpioInt() or similar.
179
180The driver can call the function - fwnode_irq_get_byname() with the fwnode
181and interrupt name as arguments to get the corresponding IRQ number.
182
183SPI serial bus support
184======================
185
186Slave devices behind SPI bus have SpiSerialBus resource attached to them.
187This is extracted automatically by the SPI core and the slave devices are
188enumerated once spi_register_master() is called by the bus driver.
189
190Here is what the ACPI namespace for a SPI slave might look like::
191
192	Device (EEP0)
193	{
194		Name (_ADR, 1)
195		Name (_CID, Package () {
196			"ATML0025",
197			"AT25",
198		})
199		...
200		Method (_CRS, 0, NotSerialized)
201		{
202			SPISerialBus(1, PolarityLow, FourWireMode, 8,
203				ControllerInitiated, 1000000, ClockPolarityLow,
204				ClockPhaseFirst, "\\_SB.PCI0.SPI1",)
205		}
206		...
207
208The SPI device drivers only need to add ACPI IDs in a similar way than with
209the platform device drivers. Below is an example where we add ACPI support
210to at25 SPI eeprom driver (this is meant for the above ACPI snippet)::
211
212	static const struct acpi_device_id at25_acpi_match[] = {
213		{ "AT25", 0 },
214		{ }
215	};
216	MODULE_DEVICE_TABLE(acpi, at25_acpi_match);
217
218	static struct spi_driver at25_driver = {
219		.driver = {
220			...
221			.acpi_match_table = at25_acpi_match,
222		},
223	};
224
225Note that this driver actually needs more information like page size of the
226eeprom, etc. This information can be passed via _DSD method like::
227
228	Device (EEP0)
229	{
230		...
231		Name (_DSD, Package ()
232		{
233			ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
234			Package ()
235			{
236				Package () { "size", 1024 },
237				Package () { "pagesize", 32 },
238				Package () { "address-width", 16 },
239			}
240		})
241	}
242
243Then the at25 SPI driver can get this configuration by calling device property
244APIs during ->probe() phase like::
245
246	err = device_property_read_u32(dev, "size", &size);
247	if (err)
248		...error handling...
249
250	err = device_property_read_u32(dev, "pagesize", &page_size);
251	if (err)
252		...error handling...
253
254	err = device_property_read_u32(dev, "address-width", &addr_width);
255	if (err)
256		...error handling...
257
258I2C serial bus support
259======================
260
261The slaves behind I2C bus controller only need to add the ACPI IDs like
262with the platform and SPI drivers. The I2C core automatically enumerates
263any slave devices behind the controller device once the adapter is
264registered.
265
266Below is an example of how to add ACPI support to the existing mpu3050
267input driver::
268
269	static const struct acpi_device_id mpu3050_acpi_match[] = {
270		{ "MPU3050", 0 },
271		{ }
272	};
273	MODULE_DEVICE_TABLE(acpi, mpu3050_acpi_match);
274
275	static struct i2c_driver mpu3050_i2c_driver = {
276		.driver	= {
277			.name	= "mpu3050",
278			.pm	= &mpu3050_pm,
279			.of_match_table = mpu3050_of_match,
280			.acpi_match_table = mpu3050_acpi_match,
281		},
282		.probe		= mpu3050_probe,
283		.remove		= mpu3050_remove,
284		.id_table	= mpu3050_ids,
285	};
286	module_i2c_driver(mpu3050_i2c_driver);
287
288Reference to PWM device
289=======================
290
291Sometimes a device can be a consumer of PWM channel. Obviously OS would like
292to know which one. To provide this mapping the special property has been
293introduced, i.e.::
294
295    Device (DEV)
296    {
297        Name (_DSD, Package ()
298        {
299            ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
300            Package () {
301                Package () { "compatible", Package () { "pwm-leds" } },
302                Package () { "label", "alarm-led" },
303                Package () { "pwms",
304                    Package () {
305                        "\\_SB.PCI0.PWM",  // <PWM device reference>
306                        0,                 // <PWM index>
307                        600000000,         // <PWM period>
308                        0,                 // <PWM flags>
309                    }
310                }
311            }
312        })
313        ...
314    }
315
316In the above example the PWM-based LED driver references to the PWM channel 0
317of \_SB.PCI0.PWM device with initial period setting equal to 600 ms (note that
318value is given in nanoseconds).
319
320GPIO support
321============
322
323ACPI 5 introduced two new resources to describe GPIO connections: GpioIo
324and GpioInt. These resources can be used to pass GPIO numbers used by
325the device to the driver. ACPI 5.1 extended this with _DSD (Device
326Specific Data) which made it possible to name the GPIOs among other things.
327
328For example::
329
330	Device (DEV)
331	{
332		Method (_CRS, 0, NotSerialized)
333		{
334			Name (SBUF, ResourceTemplate()
335			{
336				// Used to power on/off the device
337				GpioIo (Exclusive, PullNone, 0, 0, IoRestrictionOutputOnly,
338					"\\_SB.PCI0.GPI0", 0, ResourceConsumer) { 85 }
339
340				// Interrupt for the device
341				GpioInt (Edge, ActiveHigh, ExclusiveAndWake, PullNone, 0,
342					 "\\_SB.PCI0.GPI0", 0, ResourceConsumer) { 88 }
343			}
344
345			Return (SBUF)
346		}
347
348		// ACPI 5.1 _DSD used for naming the GPIOs
349		Name (_DSD, Package ()
350		{
351			ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
352			Package ()
353			{
354				Package () { "power-gpios", Package () { ^DEV, 0, 0, 0 } },
355				Package () { "irq-gpios", Package () { ^DEV, 1, 0, 0 } },
356			}
357		})
358		...
359	}
360
361These GPIO numbers are controller relative and path "\\_SB.PCI0.GPI0"
362specifies the path to the controller. In order to use these GPIOs in Linux
363we need to translate them to the corresponding Linux GPIO descriptors.
364
365There is a standard GPIO API for that and is documented in
366Documentation/admin-guide/gpio/.
367
368In the above example we can get the corresponding two GPIO descriptors with
369a code like this::
370
371	#include <linux/gpio/consumer.h>
372	...
373
374	struct gpio_desc *irq_desc, *power_desc;
375
376	irq_desc = gpiod_get(dev, "irq");
377	if (IS_ERR(irq_desc))
378		/* handle error */
379
380	power_desc = gpiod_get(dev, "power");
381	if (IS_ERR(power_desc))
382		/* handle error */
383
384	/* Now we can use the GPIO descriptors */
385
386There are also devm_* versions of these functions which release the
387descriptors once the device is released.
388
389See Documentation/firmware-guide/acpi/gpio-properties.rst for more information
390about the _DSD binding related to GPIOs.
391
392RS-485 support
393==============
394
395ACPI _DSD (Device Specific Data) can be used to describe RS-485 capability
396of UART.
397
398For example::
399
400	Device (DEV)
401	{
402		...
403
404		// ACPI 5.1 _DSD used for RS-485 capabilities
405		Name (_DSD, Package ()
406		{
407			ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
408			Package ()
409			{
410				Package () {"rs485-rts-active-low", Zero},
411				Package () {"rs485-rx-active-high", Zero},
412				Package () {"rs485-rx-during-tx", Zero},
413			}
414		})
415		...
416
417MFD devices
418===========
419
420The MFD devices register their children as platform devices. For the child
421devices there needs to be an ACPI handle that they can use to reference
422parts of the ACPI namespace that relate to them. In the Linux MFD subsystem
423we provide two ways:
424
425  - The children share the parent ACPI handle.
426  - The MFD cell can specify the ACPI id of the device.
427
428For the first case, the MFD drivers do not need to do anything. The
429resulting child platform device will have its ACPI_COMPANION() set to point
430to the parent device.
431
432If the ACPI namespace has a device that we can match using an ACPI id or ACPI
433adr, the cell should be set like::
434
435	static struct mfd_cell_acpi_match my_subdevice_cell_acpi_match = {
436		.pnpid = "XYZ0001",
437		.adr = 0,
438	};
439
440	static struct mfd_cell my_subdevice_cell = {
441		.name = "my_subdevice",
442		/* set the resources relative to the parent */
443		.acpi_match = &my_subdevice_cell_acpi_match,
444	};
445
446The ACPI id "XYZ0001" is then used to lookup an ACPI device directly under
447the MFD device and if found, that ACPI companion device is bound to the
448resulting child platform device.
449
450Device Tree namespace link device ID
451====================================
452
453The Device Tree protocol uses device identification based on the "compatible"
454property whose value is a string or an array of strings recognized as device
455identifiers by drivers and the driver core.  The set of all those strings may be
456regarded as a device identification namespace analogous to the ACPI/PNP device
457ID namespace.  Consequently, in principle it should not be necessary to allocate
458a new (and arguably redundant) ACPI/PNP device ID for a devices with an existing
459identification string in the Device Tree (DT) namespace, especially if that ID
460is only needed to indicate that a given device is compatible with another one,
461presumably having a matching driver in the kernel already.
462
463In ACPI, the device identification object called _CID (Compatible ID) is used to
464list the IDs of devices the given one is compatible with, but those IDs must
465belong to one of the namespaces prescribed by the ACPI specification (see
466Section 6.1.2 of ACPI 6.0 for details) and the DT namespace is not one of them.
467Moreover, the specification mandates that either a _HID or an _ADR identification
468object be present for all ACPI objects representing devices (Section 6.1 of ACPI
4696.0).  For non-enumerable bus types that object must be _HID and its value must
470be a device ID from one of the namespaces prescribed by the specification too.
471
472The special DT namespace link device ID, PRP0001, provides a means to use the
473existing DT-compatible device identification in ACPI and to satisfy the above
474requirements following from the ACPI specification at the same time.  Namely,
475if PRP0001 is returned by _HID, the ACPI subsystem will look for the
476"compatible" property in the device object's _DSD and will use the value of that
477property to identify the corresponding device in analogy with the original DT
478device identification algorithm.  If the "compatible" property is not present
479or its value is not valid, the device will not be enumerated by the ACPI
480subsystem.  Otherwise, it will be enumerated automatically as a platform device
481(except when an I2C or SPI link from the device to its parent is present, in
482which case the ACPI core will leave the device enumeration to the parent's
483driver) and the identification strings from the "compatible" property value will
484be used to find a driver for the device along with the device IDs listed by _CID
485(if present).
486
487Analogously, if PRP0001 is present in the list of device IDs returned by _CID,
488the identification strings listed by the "compatible" property value (if present
489and valid) will be used to look for a driver matching the device, but in that
490case their relative priority with respect to the other device IDs listed by
491_HID and _CID depends on the position of PRP0001 in the _CID return package.
492Specifically, the device IDs returned by _HID and preceding PRP0001 in the _CID
493return package will be checked first.  Also in that case the bus type the device
494will be enumerated to depends on the device ID returned by _HID.
495
496For example, the following ACPI sample might be used to enumerate an lm75-type
497I2C temperature sensor and match it to the driver using the Device Tree
498namespace link::
499
500	Device (TMP0)
501	{
502		Name (_HID, "PRP0001")
503		Name (_DSD, Package () {
504			ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
505			Package () {
506				Package () { "compatible", "ti,tmp75" },
507			}
508		})
509		Method (_CRS, 0, Serialized)
510		{
511			Name (SBUF, ResourceTemplate ()
512			{
513				I2cSerialBusV2 (0x48, ControllerInitiated,
514					400000, AddressingMode7Bit,
515					"\\_SB.PCI0.I2C1", 0x00,
516					ResourceConsumer, , Exclusive,)
517			})
518			Return (SBUF)
519		}
520	}
521
522It is valid to define device objects with a _HID returning PRP0001 and without
523the "compatible" property in the _DSD or a _CID as long as one of their
524ancestors provides a _DSD with a valid "compatible" property.  Such device
525objects are then simply regarded as additional "blocks" providing hierarchical
526configuration information to the driver of the composite ancestor device.
527
528However, PRP0001 can only be returned from either _HID or _CID of a device
529object if all of the properties returned by the _DSD associated with it (either
530the _DSD of the device object itself or the _DSD of its ancestor in the
531"composite device" case described above) can be used in the ACPI environment.
532Otherwise, the _DSD itself is regarded as invalid and therefore the "compatible"
533property returned by it is meaningless.
534
535Refer to Documentation/firmware-guide/acpi/DSD-properties-rules.rst for more
536information.
537
538PCI hierarchy representation
539============================
540
541Sometimes could be useful to enumerate a PCI device, knowing its position on the
542PCI bus.
543
544For example, some systems use PCI devices soldered directly on the mother board,
545in a fixed position (ethernet, Wi-Fi, serial ports, etc.). In this conditions it
546is possible to refer to these PCI devices knowing their position on the PCI bus
547topology.
548
549To identify a PCI device, a complete hierarchical description is required, from
550the chipset root port to the final device, through all the intermediate
551bridges/switches of the board.
552
553For example, let us assume to have a system with a PCIe serial port, an
554Exar XR17V3521, soldered on the main board. This UART chip also includes
55516 GPIOs and we want to add the property ``gpio-line-names`` [1] to these pins.
556In this case, the ``lspci`` output for this component is::
557
558	07:00.0 Serial controller: Exar Corp. XR17V3521 Dual PCIe UART (rev 03)
559
560The complete ``lspci`` output (manually reduced in length) is::
561
562	00:00.0 Host bridge: Intel Corp... Host Bridge (rev 0d)
563	...
564	00:13.0 PCI bridge: Intel Corp... PCI Express Port A #1 (rev fd)
565	00:13.1 PCI bridge: Intel Corp... PCI Express Port A #2 (rev fd)
566	00:13.2 PCI bridge: Intel Corp... PCI Express Port A #3 (rev fd)
567	00:14.0 PCI bridge: Intel Corp... PCI Express Port B #1 (rev fd)
568	00:14.1 PCI bridge: Intel Corp... PCI Express Port B #2 (rev fd)
569	...
570	05:00.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
571	06:01.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
572	06:02.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
573	06:03.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
574	07:00.0 Serial controller: Exar Corp. XR17V3521 Dual PCIe UART (rev 03) <-- Exar
575	...
576
577The bus topology is::
578
579	-[0000:00]-+-00.0
580	           ...
581	           +-13.0-[01]----00.0
582	           +-13.1-[02]----00.0
583	           +-13.2-[03]--
584	           +-14.0-[04]----00.0
585	           +-14.1-[05-09]----00.0-[06-09]--+-01.0-[07]----00.0 <-- Exar
586	           |                               +-02.0-[08]----00.0
587	           |                               \-03.0-[09]--
588	           ...
589	           \-1f.1
590
591To describe this Exar device on the PCI bus, we must start from the ACPI name
592of the chipset bridge (also called "root port") with address::
593
594	Bus: 0 - Device: 14 - Function: 1
595
596To find this information is necessary disassemble the BIOS ACPI tables, in
597particular the DSDT (see also [2])::
598
599	mkdir ~/tables/
600	cd ~/tables/
601	acpidump > acpidump
602	acpixtract -a acpidump
603	iasl -e ssdt?.* -d dsdt.dat
604
605Now, in the dsdt.dsl, we have to search the device whose address is related to
6060x14 (device) and 0x01 (function). In this case we can find the following
607device::
608
609	Scope (_SB.PCI0)
610	{
611	... other definitions follow ...
612		Device (RP02)
613		{
614			Method (_ADR, 0, NotSerialized)  // _ADR: Address
615			{
616				If ((RPA2 != Zero))
617				{
618					Return (RPA2) /* \RPA2 */
619				}
620				Else
621				{
622					Return (0x00140001)
623				}
624			}
625	... other definitions follow ...
626
627and the _ADR method [3] returns exactly the device/function couple that
628we are looking for. With this information and analyzing the above ``lspci``
629output (both the devices list and the devices tree), we can write the following
630ACPI description for the Exar PCIe UART, also adding the list of its GPIO line
631names::
632
633	Scope (_SB.PCI0.RP02)
634	{
635		Device (BRG1) //Bridge
636		{
637			Name (_ADR, 0x0000)
638
639			Device (BRG2) //Bridge
640			{
641				Name (_ADR, 0x00010000)
642
643				Device (EXAR)
644				{
645					Name (_ADR, 0x0000)
646
647					Name (_DSD, Package ()
648					{
649						ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
650						Package ()
651						{
652							Package ()
653							{
654								"gpio-line-names",
655								Package ()
656								{
657									"mode_232",
658									"mode_422",
659									"mode_485",
660									"misc_1",
661									"misc_2",
662									"misc_3",
663									"",
664									"",
665									"aux_1",
666									"aux_2",
667									"aux_3",
668								}
669							}
670						}
671					})
672				}
673			}
674		}
675	}
676
677The location "_SB.PCI0.RP02" is obtained by the above investigation in the
678dsdt.dsl table, whereas the device names "BRG1", "BRG2" and "EXAR" are
679created analyzing the position of the Exar UART in the PCI bus topology.
680
681References
682==========
683
684[1] Documentation/firmware-guide/acpi/gpio-properties.rst
685
686[2] Documentation/admin-guide/acpi/initrd_table_override.rst
687
688[3] ACPI Specifications, Version 6.3 - Paragraph 6.1.1 _ADR Address)
689    https://uefi.org/sites/default/files/resources/ACPI_6_3_May16.pdf,
690    referenced 2020-11-18
691