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59c39878 MW |
1 | ACPI based device enumeration |
2 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
3 | ACPI 5 introduced a set of new resources (UartTSerialBus, I2cSerialBus, | |
4 | SpiSerialBus, GpioIo and GpioInt) which can be used in enumerating slave | |
5 | devices behind serial bus controllers. | |
6 | ||
7 | In addition we are starting to see peripherals integrated in the | |
8 | SoC/Chipset to appear only in ACPI namespace. These are typically devices | |
9 | that are accessed through memory-mapped registers. | |
10 | ||
11 | In order to support this and re-use the existing drivers as much as | |
12 | possible we decided to do following: | |
13 | ||
14 | o Devices that have no bus connector resource are represented as | |
15 | platform devices. | |
16 | ||
17 | o Devices behind real busses where there is a connector resource | |
18 | are represented as struct spi_device or struct i2c_device | |
19 | (standard UARTs are not busses so there is no struct uart_device). | |
20 | ||
21 | As both ACPI and Device Tree represent a tree of devices (and their | |
22 | resources) this implementation follows the Device Tree way as much as | |
23 | possible. | |
24 | ||
25 | The ACPI implementation enumerates devices behind busses (platform, SPI and | |
26 | I2C), creates the physical devices and binds them to their ACPI handle in | |
27 | the ACPI namespace. | |
28 | ||
29 | This means that when ACPI_HANDLE(dev) returns non-NULL the device was | |
30 | enumerated from ACPI namespace. This handle can be used to extract other | |
31 | device-specific configuration. There is an example of this below. | |
32 | ||
33 | Platform bus support | |
34 | ~~~~~~~~~~~~~~~~~~~~ | |
35 | Since we are using platform devices to represent devices that are not | |
36 | connected to any physical bus we only need to implement a platform driver | |
37 | for the device and add supported ACPI IDs. If this same IP-block is used on | |
38 | some other non-ACPI platform, the driver might work out of the box or needs | |
39 | some minor changes. | |
40 | ||
41 | Adding ACPI support for an existing driver should be pretty | |
42 | straightforward. Here is the simplest example: | |
43 | ||
44 | #ifdef CONFIG_ACPI | |
45 | static struct acpi_device_id mydrv_acpi_match[] = { | |
46 | /* ACPI IDs here */ | |
47 | { } | |
48 | }; | |
49 | MODULE_DEVICE_TABLE(acpi, mydrv_acpi_match); | |
50 | #endif | |
51 | ||
52 | static struct platform_driver my_driver = { | |
53 | ... | |
54 | .driver = { | |
55 | .acpi_match_table = ACPI_PTR(mydrv_acpi_match), | |
56 | }, | |
57 | }; | |
58 | ||
59 | If the driver needs to perform more complex initialization like getting and | |
60 | configuring GPIOs it can get its ACPI handle and extract this information | |
61 | from ACPI tables. | |
62 | ||
1b2e98bc AS |
63 | DMA support |
64 | ~~~~~~~~~~~ | |
65 | DMA controllers enumerated via ACPI should be registered in the system to | |
66 | provide generic access to their resources. For example, a driver that would | |
67 | like to be accessible to slave devices via generic API call | |
68 | dma_request_slave_channel() must register itself at the end of the probe | |
69 | function like this: | |
70 | ||
71 | err = devm_acpi_dma_controller_register(dev, xlate_func, dw); | |
72 | /* Handle the error if it's not a case of !CONFIG_ACPI */ | |
73 | ||
74 | and implement custom xlate function if needed (usually acpi_dma_simple_xlate() | |
75 | is enough) which converts the FixedDMA resource provided by struct | |
76 | acpi_dma_spec into the corresponding DMA channel. A piece of code for that case | |
77 | could look like: | |
78 | ||
79 | #ifdef CONFIG_ACPI | |
80 | struct filter_args { | |
81 | /* Provide necessary information for the filter_func */ | |
82 | ... | |
83 | }; | |
84 | ||
85 | static bool filter_func(struct dma_chan *chan, void *param) | |
86 | { | |
87 | /* Choose the proper channel */ | |
88 | ... | |
89 | } | |
90 | ||
91 | static struct dma_chan *xlate_func(struct acpi_dma_spec *dma_spec, | |
92 | struct acpi_dma *adma) | |
93 | { | |
94 | dma_cap_mask_t cap; | |
95 | struct filter_args args; | |
96 | ||
97 | /* Prepare arguments for filter_func */ | |
98 | ... | |
99 | return dma_request_channel(cap, filter_func, &args); | |
100 | } | |
101 | #else | |
102 | static struct dma_chan *xlate_func(struct acpi_dma_spec *dma_spec, | |
103 | struct acpi_dma *adma) | |
104 | { | |
105 | return NULL; | |
106 | } | |
107 | #endif | |
108 | ||
109 | dma_request_slave_channel() will call xlate_func() for each registered DMA | |
110 | controller. In the xlate function the proper channel must be chosen based on | |
111 | information in struct acpi_dma_spec and the properties of the controller | |
112 | provided by struct acpi_dma. | |
113 | ||
114 | Clients must call dma_request_slave_channel() with the string parameter that | |
115 | corresponds to a specific FixedDMA resource. By default "tx" means the first | |
116 | entry of the FixedDMA resource array, "rx" means the second entry. The table | |
117 | below shows a layout: | |
118 | ||
119 | Device (I2C0) | |
120 | { | |
121 | ... | |
122 | Method (_CRS, 0, NotSerialized) | |
123 | { | |
124 | Name (DBUF, ResourceTemplate () | |
125 | { | |
126 | FixedDMA (0x0018, 0x0004, Width32bit, _Y48) | |
127 | FixedDMA (0x0019, 0x0005, Width32bit, ) | |
128 | }) | |
129 | ... | |
130 | } | |
131 | } | |
132 | ||
133 | So, the FixedDMA with request line 0x0018 is "tx" and next one is "rx" in | |
134 | this example. | |
135 | ||
136 | In robust cases the client unfortunately needs to call | |
137 | acpi_dma_request_slave_chan_by_index() directly and therefore choose the | |
138 | specific FixedDMA resource by its index. | |
139 | ||
59c39878 MW |
140 | SPI serial bus support |
141 | ~~~~~~~~~~~~~~~~~~~~~~ | |
142 | Slave devices behind SPI bus have SpiSerialBus resource attached to them. | |
143 | This is extracted automatically by the SPI core and the slave devices are | |
144 | enumerated once spi_register_master() is called by the bus driver. | |
145 | ||
146 | Here is what the ACPI namespace for a SPI slave might look like: | |
147 | ||
148 | Device (EEP0) | |
149 | { | |
150 | Name (_ADR, 1) | |
151 | Name (_CID, Package() { | |
152 | "ATML0025", | |
153 | "AT25", | |
154 | }) | |
155 | ... | |
156 | Method (_CRS, 0, NotSerialized) | |
157 | { | |
158 | SPISerialBus(1, PolarityLow, FourWireMode, 8, | |
159 | ControllerInitiated, 1000000, ClockPolarityLow, | |
160 | ClockPhaseFirst, "\\_SB.PCI0.SPI1",) | |
161 | } | |
162 | ... | |
163 | ||
164 | The SPI device drivers only need to add ACPI IDs in a similar way than with | |
165 | the platform device drivers. Below is an example where we add ACPI support | |
166 | to at25 SPI eeprom driver (this is meant for the above ACPI snippet): | |
167 | ||
168 | #ifdef CONFIG_ACPI | |
169 | static struct acpi_device_id at25_acpi_match[] = { | |
170 | { "AT25", 0 }, | |
171 | { }, | |
172 | }; | |
173 | MODULE_DEVICE_TABLE(acpi, at25_acpi_match); | |
174 | #endif | |
175 | ||
176 | static struct spi_driver at25_driver = { | |
177 | .driver = { | |
178 | ... | |
179 | .acpi_match_table = ACPI_PTR(at25_acpi_match), | |
180 | }, | |
181 | }; | |
182 | ||
183 | Note that this driver actually needs more information like page size of the | |
184 | eeprom etc. but at the time writing this there is no standard way of | |
185 | passing those. One idea is to return this in _DSM method like: | |
186 | ||
187 | Device (EEP0) | |
188 | { | |
189 | ... | |
190 | Method (_DSM, 4, NotSerialized) | |
191 | { | |
192 | Store (Package (6) | |
193 | { | |
194 | "byte-len", 1024, | |
195 | "addr-mode", 2, | |
196 | "page-size, 32 | |
197 | }, Local0) | |
198 | ||
199 | // Check UUIDs etc. | |
200 | ||
201 | Return (Local0) | |
202 | } | |
203 | ||
2d6674b8 | 204 | Then the at25 SPI driver can get this configuration by calling _DSM on its |
59c39878 MW |
205 | ACPI handle like: |
206 | ||
207 | struct acpi_buffer output = { ACPI_ALLOCATE_BUFFER, NULL }; | |
208 | struct acpi_object_list input; | |
209 | acpi_status status; | |
210 | ||
211 | /* Fill in the input buffer */ | |
212 | ||
213 | status = acpi_evaluate_object(ACPI_HANDLE(&spi->dev), "_DSM", | |
214 | &input, &output); | |
215 | if (ACPI_FAILURE(status)) | |
216 | /* Handle the error */ | |
217 | ||
218 | /* Extract the data here */ | |
219 | ||
220 | kfree(output.pointer); | |
221 | ||
222 | I2C serial bus support | |
223 | ~~~~~~~~~~~~~~~~~~~~~~ | |
224 | The slaves behind I2C bus controller only need to add the ACPI IDs like | |
55e71edb MW |
225 | with the platform and SPI drivers. The I2C core automatically enumerates |
226 | any slave devices behind the controller device once the adapter is | |
227 | registered. | |
59c39878 MW |
228 | |
229 | Below is an example of how to add ACPI support to the existing mpu3050 | |
230 | input driver: | |
231 | ||
232 | #ifdef CONFIG_ACPI | |
233 | static struct acpi_device_id mpu3050_acpi_match[] = { | |
234 | { "MPU3050", 0 }, | |
235 | { }, | |
236 | }; | |
237 | MODULE_DEVICE_TABLE(acpi, mpu3050_acpi_match); | |
238 | #endif | |
239 | ||
240 | static struct i2c_driver mpu3050_i2c_driver = { | |
241 | .driver = { | |
242 | .name = "mpu3050", | |
243 | .owner = THIS_MODULE, | |
244 | .pm = &mpu3050_pm, | |
245 | .of_match_table = mpu3050_of_match, | |
de14da2a | 246 | .acpi_match_table = ACPI_PTR(mpu3050_acpi_match), |
59c39878 MW |
247 | }, |
248 | .probe = mpu3050_probe, | |
63a29f74 | 249 | .remove = mpu3050_remove, |
59c39878 MW |
250 | .id_table = mpu3050_ids, |
251 | }; | |
252 | ||
253 | GPIO support | |
254 | ~~~~~~~~~~~~ | |
255 | ACPI 5 introduced two new resources to describe GPIO connections: GpioIo | |
256 | and GpioInt. These resources are used be used to pass GPIO numbers used by | |
257 | the device to the driver. For example: | |
258 | ||
259 | Method (_CRS, 0, NotSerialized) | |
260 | { | |
261 | Name (SBUF, ResourceTemplate() | |
262 | { | |
12028d2d MW |
263 | ... |
264 | // Used to power on/off the device | |
59c39878 MW |
265 | GpioIo (Exclusive, PullDefault, 0x0000, 0x0000, |
266 | IoRestrictionOutputOnly, "\\_SB.PCI0.GPI0", | |
267 | 0x00, ResourceConsumer,,) | |
268 | { | |
269 | // Pin List | |
270 | 0x0055 | |
271 | } | |
12028d2d MW |
272 | |
273 | // Interrupt for the device | |
274 | GpioInt (Edge, ActiveHigh, ExclusiveAndWake, PullNone, | |
275 | 0x0000, "\\_SB.PCI0.GPI0", 0x00, ResourceConsumer,,) | |
276 | { | |
277 | // Pin list | |
278 | 0x0058 | |
279 | } | |
280 | ||
59c39878 MW |
281 | ... |
282 | ||
59c39878 | 283 | } |
12028d2d MW |
284 | |
285 | Return (SBUF) | |
59c39878 MW |
286 | } |
287 | ||
288 | These GPIO numbers are controller relative and path "\\_SB.PCI0.GPI0" | |
289 | specifies the path to the controller. In order to use these GPIOs in Linux | |
ccb6fbb9 | 290 | we need to translate them to the corresponding Linux GPIO descriptors. |
59c39878 | 291 | |
ccb6fbb9 | 292 | There is a standard GPIO API for that and is documented in |
51caa05a | 293 | Documentation/gpio/. |
12028d2d | 294 | |
ccb6fbb9 MW |
295 | In the above example we can get the corresponding two GPIO descriptors with |
296 | a code like this: | |
45f39439 MW |
297 | |
298 | #include <linux/gpio/consumer.h> | |
299 | ... | |
300 | ||
301 | struct gpio_desc *irq_desc, *power_desc; | |
302 | ||
303 | irq_desc = gpiod_get_index(dev, NULL, 1); | |
304 | if (IS_ERR(irq_desc)) | |
305 | /* handle error */ | |
306 | ||
307 | power_desc = gpiod_get_index(dev, NULL, 0); | |
308 | if (IS_ERR(power_desc)) | |
309 | /* handle error */ | |
310 | ||
311 | /* Now we can use the GPIO descriptors */ | |
312 | ||
ccb6fbb9 MW |
313 | There are also devm_* versions of these functions which release the |
314 | descriptors once the device is released. | |
6ab34301 MW |
315 | |
316 | MFD devices | |
317 | ~~~~~~~~~~~ | |
318 | The MFD devices register their children as platform devices. For the child | |
319 | devices there needs to be an ACPI handle that they can use to reference | |
320 | parts of the ACPI namespace that relate to them. In the Linux MFD subsystem | |
321 | we provide two ways: | |
322 | ||
323 | o The children share the parent ACPI handle. | |
324 | o The MFD cell can specify the ACPI id of the device. | |
325 | ||
326 | For the first case, the MFD drivers do not need to do anything. The | |
327 | resulting child platform device will have its ACPI_COMPANION() set to point | |
328 | to the parent device. | |
329 | ||
330 | If the ACPI namespace has a device that we can match using an ACPI id, | |
331 | the id should be set like: | |
332 | ||
333 | static struct mfd_cell my_subdevice_cell = { | |
334 | .name = "my_subdevice", | |
335 | /* set the resources relative to the parent */ | |
336 | .acpi_pnpid = "XYZ0001", | |
337 | }; | |
338 | ||
339 | The ACPI id "XYZ0001" is then used to lookup an ACPI device directly under | |
340 | the MFD device and if found, that ACPI companion device is bound to the | |
341 | resulting child platform device. |