1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 ====================================== 3 ======================================
4 _DSD Device Properties Related to GPIO 4 _DSD Device Properties Related to GPIO
5 ====================================== 5 ======================================
6 6
7 With the release of ACPI 5.1, the _DSD configu 7 With the release of ACPI 5.1, the _DSD configuration object finally
8 allows names to be given to GPIOs (and other t 8 allows names to be given to GPIOs (and other things as well) returned
9 by _CRS. Previously, we were only able to use 9 by _CRS. Previously, we were only able to use an integer index to find
10 the corresponding GPIO, which is pretty error 10 the corresponding GPIO, which is pretty error prone (it depends on
11 the _CRS output ordering, for example). 11 the _CRS output ordering, for example).
12 12
13 With _DSD we can now query GPIOs using a name 13 With _DSD we can now query GPIOs using a name instead of an integer
14 index, like the ASL example below shows:: 14 index, like the ASL example below shows::
15 15
16 // Bluetooth device with reset and shutdown 16 // Bluetooth device with reset and shutdown GPIOs
17 Device (BTH) 17 Device (BTH)
18 { 18 {
19 Name (_HID, ...) 19 Name (_HID, ...)
20 20
21 Name (_CRS, ResourceTemplate () 21 Name (_CRS, ResourceTemplate ()
22 { 22 {
23 GpioIo (Exclusive, PullUp, 0, 0, IoR 23 GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly,
24 "\\_SB.GPO0", 0, ResourceCon 24 "\\_SB.GPO0", 0, ResourceConsumer) { 15 }
25 GpioIo (Exclusive, PullUp, 0, 0, IoR 25 GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly,
26 "\\_SB.GPO0", 0, ResourceCon 26 "\\_SB.GPO0", 0, ResourceConsumer) { 27, 31 }
27 }) 27 })
28 28
29 Name (_DSD, Package () 29 Name (_DSD, Package ()
30 { 30 {
31 ToUUID("daffd814-6eba-4d8c-8a91-bc9b 31 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
32 Package () 32 Package ()
33 { 33 {
34 Package () { "reset-gpios", Pack 34 Package () { "reset-gpios", Package () { ^BTH, 1, 1, 0 } },
35 Package () { "shutdown-gpios", P 35 Package () { "shutdown-gpios", Package () { ^BTH, 0, 0, 0 } },
36 } 36 }
37 }) 37 })
38 } 38 }
39 39
40 The format of the supported GPIO property is:: 40 The format of the supported GPIO property is::
41 41
42 Package () { "name", Package () { ref, index 42 Package () { "name", Package () { ref, index, pin, active_low }}
43 43
44 ref 44 ref
45 The device that has _CRS containing GpioIo() 45 The device that has _CRS containing GpioIo()/GpioInt() resources,
46 typically this is the device itself (BTH in 46 typically this is the device itself (BTH in our case).
47 index 47 index
48 Index of the GpioIo()/GpioInt() resource in 48 Index of the GpioIo()/GpioInt() resource in _CRS starting from zero.
49 pin 49 pin
50 Pin in the GpioIo()/GpioInt() resource. Typi 50 Pin in the GpioIo()/GpioInt() resource. Typically this is zero.
51 active_low 51 active_low
52 If 1, the GPIO is marked as active_low. 52 If 1, the GPIO is marked as active_low.
53 53
54 Since ACPI GpioIo() resource does not have a f 54 Since ACPI GpioIo() resource does not have a field saying whether it is
55 active low or high, the "active_low" argument 55 active low or high, the "active_low" argument can be used here. Setting
56 it to 1 marks the GPIO as active low. 56 it to 1 marks the GPIO as active low.
57 57
58 Note, active_low in _DSD does not make sense f 58 Note, active_low in _DSD does not make sense for GpioInt() resource and
59 must be 0. GpioInt() resource has its own mean 59 must be 0. GpioInt() resource has its own means of defining it.
60 60
61 In our Bluetooth example the "reset-gpios" ref 61 In our Bluetooth example the "reset-gpios" refers to the second GpioIo()
62 resource, second pin in that resource with the 62 resource, second pin in that resource with the GPIO number of 31.
63 63
64 The GpioIo() resource unfortunately doesn't ex 64 The GpioIo() resource unfortunately doesn't explicitly provide an initial
65 state of the output pin which driver should us 65 state of the output pin which driver should use during its initialization.
66 66
67 Linux tries to use common sense here and deriv 67 Linux tries to use common sense here and derives the state from the bias
68 and polarity settings. The table below shows t 68 and polarity settings. The table below shows the expectations:
69 69
70 +-------------+-------------+----------------- 70 +-------------+-------------+-----------------------------------------------+
71 | Pull Bias | Polarity | Requested... 71 | Pull Bias | Polarity | Requested... |
72 +=============+=============+================= 72 +=============+=============+===============================================+
73 | Implicit 73 | Implicit |
74 +-------------+-------------+----------------- 74 +-------------+-------------+-----------------------------------------------+
75 | **Default** | x | AS IS (assumed f 75 | **Default** | x | AS IS (assumed firmware configured it for us) |
76 +-------------+-------------+----------------- 76 +-------------+-------------+-----------------------------------------------+
77 | Explicit 77 | Explicit |
78 +-------------+-------------+----------------- 78 +-------------+-------------+-----------------------------------------------+
79 | **None** | x | AS IS (assumed f 79 | **None** | x | AS IS (assumed firmware configured it for us) |
80 | | | with no Pull Bia 80 | | | with no Pull Bias |
81 +-------------+-------------+----------------- 81 +-------------+-------------+-----------------------------------------------+
82 | **Up** | x (no _DSD) | 82 | **Up** | x (no _DSD) | |
83 | +-------------+ as high, assumin 83 | +-------------+ as high, assuming non-active |
84 | | Low | 84 | | Low | |
85 | +-------------+----------------- 85 | +-------------+-----------------------------------------------+
86 | | High | as high, assumin 86 | | High | as high, assuming active |
87 +-------------+-------------+----------------- 87 +-------------+-------------+-----------------------------------------------+
88 | **Down** | x (no _DSD) | 88 | **Down** | x (no _DSD) | |
89 | +-------------+ as low, assuming 89 | +-------------+ as low, assuming non-active |
90 | | High | 90 | | High | |
91 | +-------------+----------------- 91 | +-------------+-----------------------------------------------+
92 | | Low | as low, assuming 92 | | Low | as low, assuming active |
93 +-------------+-------------+----------------- 93 +-------------+-------------+-----------------------------------------------+
94 94
95 That said, for our above example the both GPIO 95 That said, for our above example the both GPIOs, since the bias setting
96 is explicit and _DSD is present, will be treat 96 is explicit and _DSD is present, will be treated as active with a high
97 polarity and Linux will configure the pins in 97 polarity and Linux will configure the pins in this state until a driver
98 reprograms them differently. 98 reprograms them differently.
99 99
100 It is possible to leave holes in the array of 100 It is possible to leave holes in the array of GPIOs. This is useful in
101 cases like with SPI host controllers where som 101 cases like with SPI host controllers where some chip selects may be
102 implemented as GPIOs and some as native signal 102 implemented as GPIOs and some as native signals. For example a SPI host
103 controller can have chip selects 0 and 2 imple 103 controller can have chip selects 0 and 2 implemented as GPIOs and 1 as
104 native:: 104 native::
105 105
106 Package () { 106 Package () {
107 "cs-gpios", 107 "cs-gpios",
108 Package () { 108 Package () {
109 ^GPIO, 19, 0, 0, // chip select 0: G 109 ^GPIO, 19, 0, 0, // chip select 0: GPIO
110 0, // chip select 1: n 110 0, // chip select 1: native signal
111 ^GPIO, 20, 0, 0, // chip select 2: G 111 ^GPIO, 20, 0, 0, // chip select 2: GPIO
112 } 112 }
113 } 113 }
114 114
115 Note, that historically ACPI has no means of t 115 Note, that historically ACPI has no means of the GPIO polarity and thus
116 the SPISerialBus() resource defines it on the 116 the SPISerialBus() resource defines it on the per-chip basis. In order
117 to avoid a chain of negations, the GPIO polari 117 to avoid a chain of negations, the GPIO polarity is considered being
118 Active High. Even for the cases when _DSD() is 118 Active High. Even for the cases when _DSD() is involved (see the example
119 above) the GPIO CS polarity must be defined Ac 119 above) the GPIO CS polarity must be defined Active High to avoid ambiguity.
120 120
121 Other supported properties 121 Other supported properties
122 ========================== 122 ==========================
123 123
124 Following Device Tree compatible device proper 124 Following Device Tree compatible device properties are also supported by
125 _DSD device properties for GPIO controllers: 125 _DSD device properties for GPIO controllers:
126 126
127 - gpio-hog 127 - gpio-hog
128 - output-high 128 - output-high
129 - output-low 129 - output-low
130 - input 130 - input
131 - line-name 131 - line-name
132 132
133 Example:: 133 Example::
134 134
135 Name (_DSD, Package () { 135 Name (_DSD, Package () {
136 // _DSD Hierarchical Properties Extensio 136 // _DSD Hierarchical Properties Extension UUID
137 ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a 137 ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
138 Package () { 138 Package () {
139 Package () { "hog-gpio8", "G8PU" } 139 Package () { "hog-gpio8", "G8PU" }
140 } 140 }
141 }) 141 })
142 142
143 Name (G8PU, Package () { 143 Name (G8PU, Package () {
144 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4a 144 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
145 Package () { 145 Package () {
146 Package () { "gpio-hog", 1 }, 146 Package () { "gpio-hog", 1 },
147 Package () { "gpios", Package () { 8 147 Package () { "gpios", Package () { 8, 0 } },
148 Package () { "output-high", 1 }, 148 Package () { "output-high", 1 },
149 Package () { "line-name", "gpio8-pul 149 Package () { "line-name", "gpio8-pullup" },
150 } 150 }
151 }) 151 })
152 152
153 - gpio-line-names 153 - gpio-line-names
154 154
155 The ``gpio-line-names`` declaration is a list 155 The ``gpio-line-names`` declaration is a list of strings ("names"), which
156 describes each line/pin of a GPIO controller/e 156 describes each line/pin of a GPIO controller/expander. This list, contained in
157 a package, must be inserted inside the GPIO co 157 a package, must be inserted inside the GPIO controller declaration of an ACPI
158 table (typically inside the DSDT). The ``gpio- 158 table (typically inside the DSDT). The ``gpio-line-names`` list must respect the
159 following rules (see also the examples): 159 following rules (see also the examples):
160 160
161 - the first name in the list corresponds wit 161 - the first name in the list corresponds with the first line/pin of the GPIO
162 controller/expander 162 controller/expander
163 - the names inside the list must be consecut 163 - the names inside the list must be consecutive (no "holes" are permitted)
164 - the list can be incomplete and can end bef 164 - the list can be incomplete and can end before the last GPIO line: in
165 other words, it is not mandatory to fill a 165 other words, it is not mandatory to fill all the GPIO lines
166 - empty names are allowed (two quotation mar 166 - empty names are allowed (two quotation marks ``""`` correspond to an empty
167 name) 167 name)
168 - names inside one GPIO controller/expander 168 - names inside one GPIO controller/expander must be unique
169 169
170 Example of a GPIO controller of 16 lines, with 170 Example of a GPIO controller of 16 lines, with an incomplete list with two
171 empty names:: 171 empty names::
172 172
173 Package () { 173 Package () {
174 "gpio-line-names", 174 "gpio-line-names",
175 Package () { 175 Package () {
176 "pin_0", 176 "pin_0",
177 "pin_1", 177 "pin_1",
178 "", 178 "",
179 "", 179 "",
180 "pin_3", 180 "pin_3",
181 "pin_4_push_button", 181 "pin_4_push_button",
182 } 182 }
183 } 183 }
184 184
185 At runtime, the above declaration produces the 185 At runtime, the above declaration produces the following result (using the
186 "libgpiod" tools):: 186 "libgpiod" tools)::
187 187
188 root@debian:~# gpioinfo gpiochip4 188 root@debian:~# gpioinfo gpiochip4
189 gpiochip4 - 16 lines: 189 gpiochip4 - 16 lines:
190 line 0: "pin_0" unused 190 line 0: "pin_0" unused input active-high
191 line 1: "pin_1" unused 191 line 1: "pin_1" unused input active-high
192 line 2: unnamed unused 192 line 2: unnamed unused input active-high
193 line 3: unnamed unused 193 line 3: unnamed unused input active-high
194 line 4: "pin_3" unused 194 line 4: "pin_3" unused input active-high
195 line 5: "pin_4_push_button" unused 195 line 5: "pin_4_push_button" unused input active-high
196 line 6: unnamed unused 196 line 6: unnamed unused input active-high
197 line 7 unnamed unused 197 line 7 unnamed unused input active-high
198 line 8: unnamed unused 198 line 8: unnamed unused input active-high
199 line 9: unnamed unused 199 line 9: unnamed unused input active-high
200 line 10: unnamed unused 200 line 10: unnamed unused input active-high
201 line 11: unnamed unused 201 line 11: unnamed unused input active-high
202 line 12: unnamed unused 202 line 12: unnamed unused input active-high
203 line 13: unnamed unused 203 line 13: unnamed unused input active-high
204 line 14: unnamed unused 204 line 14: unnamed unused input active-high
205 line 15: unnamed unused 205 line 15: unnamed unused input active-high
206 root@debian:~# gpiofind pin_4_push_button 206 root@debian:~# gpiofind pin_4_push_button
207 gpiochip4 5 207 gpiochip4 5
208 root@debian:~# 208 root@debian:~#
209 209
210 Another example:: 210 Another example::
211 211
212 Package () { 212 Package () {
213 "gpio-line-names", 213 "gpio-line-names",
214 Package () { 214 Package () {
215 "SPI0_CS_N", "EXP2_INT", "MUX6_IO", 215 "SPI0_CS_N", "EXP2_INT", "MUX6_IO", "UART0_RXD",
216 "MUX7_IO", "LVL_C_A1", "MUX0_IO", "S 216 "MUX7_IO", "LVL_C_A1", "MUX0_IO", "SPI1_MISO",
217 } 217 }
218 } 218 }
219 219
220 See Documentation/devicetree/bindings/gpio/gpi 220 See Documentation/devicetree/bindings/gpio/gpio.txt for more information
221 about these properties. 221 about these properties.
222 222
223 ACPI GPIO Mappings Provided by Drivers 223 ACPI GPIO Mappings Provided by Drivers
224 ====================================== 224 ======================================
225 225
226 There are systems in which the ACPI tables do 226 There are systems in which the ACPI tables do not contain _DSD but provide _CRS
227 with GpioIo()/GpioInt() resources and device d 227 with GpioIo()/GpioInt() resources and device drivers still need to work with
228 them. 228 them.
229 229
230 In those cases ACPI device identification obje 230 In those cases ACPI device identification objects, _HID, _CID, _CLS, _SUB, _HRV,
231 available to the driver can be used to identif 231 available to the driver can be used to identify the device and that is supposed
232 to be sufficient to determine the meaning and 232 to be sufficient to determine the meaning and purpose of all of the GPIO lines
233 listed by the GpioIo()/GpioInt() resources ret 233 listed by the GpioIo()/GpioInt() resources returned by _CRS. In other words,
234 the driver is supposed to know what to use the 234 the driver is supposed to know what to use the GpioIo()/GpioInt() resources for
235 once it has identified the device. Having don 235 once it has identified the device. Having done that, it can simply assign names
236 to the GPIO lines it is going to use and provi 236 to the GPIO lines it is going to use and provide the GPIO subsystem with a
237 mapping between those names and the ACPI GPIO 237 mapping between those names and the ACPI GPIO resources corresponding to them.
238 238
239 To do that, the driver needs to define a mappi 239 To do that, the driver needs to define a mapping table as a NULL-terminated
240 array of struct acpi_gpio_mapping objects that 240 array of struct acpi_gpio_mapping objects that each contains a name, a pointer
241 to an array of line data (struct acpi_gpio_par 241 to an array of line data (struct acpi_gpio_params) objects and the size of that
242 array. Each struct acpi_gpio_params object co 242 array. Each struct acpi_gpio_params object consists of three fields,
243 crs_entry_index, line_index, active_low, repre 243 crs_entry_index, line_index, active_low, representing the index of the target
244 GpioIo()/GpioInt() resource in _CRS starting f 244 GpioIo()/GpioInt() resource in _CRS starting from zero, the index of the target
245 line in that resource starting from zero, and 245 line in that resource starting from zero, and the active-low flag for that line,
246 respectively, in analogy with the _DSD GPIO pr 246 respectively, in analogy with the _DSD GPIO property format specified above.
247 247
248 For the example Bluetooth device discussed pre 248 For the example Bluetooth device discussed previously the data structures in
249 question would look like this:: 249 question would look like this::
250 250
251 static const struct acpi_gpio_params reset_g 251 static const struct acpi_gpio_params reset_gpio = { 1, 1, false };
252 static const struct acpi_gpio_params shutdow 252 static const struct acpi_gpio_params shutdown_gpio = { 0, 0, false };
253 253
254 static const struct acpi_gpio_mapping blueto 254 static const struct acpi_gpio_mapping bluetooth_acpi_gpios[] = {
255 { "reset-gpios", &reset_gpio, 1 }, 255 { "reset-gpios", &reset_gpio, 1 },
256 { "shutdown-gpios", &shutdown_gpio, 1 }, 256 { "shutdown-gpios", &shutdown_gpio, 1 },
257 { } 257 { }
258 }; 258 };
259 259
260 Next, the mapping table needs to be passed as 260 Next, the mapping table needs to be passed as the second argument to
261 acpi_dev_add_driver_gpios() or its managed ana 261 acpi_dev_add_driver_gpios() or its managed analogue that will
262 register it with the ACPI device object pointe 262 register it with the ACPI device object pointed to by its first
263 argument. That should be done in the driver's 263 argument. That should be done in the driver's .probe() routine.
264 On removal, the driver should unregister its G 264 On removal, the driver should unregister its GPIO mapping table by
265 calling acpi_dev_remove_driver_gpios() on the 265 calling acpi_dev_remove_driver_gpios() on the ACPI device object where that
266 table was previously registered. 266 table was previously registered.
267 267
268 Using the _CRS fallback 268 Using the _CRS fallback
269 ======================= 269 =======================
270 270
271 If a device does not have _DSD or the driver d 271 If a device does not have _DSD or the driver does not create ACPI GPIO
272 mapping, the Linux GPIO framework refuses to r 272 mapping, the Linux GPIO framework refuses to return any GPIOs. This is
273 because the driver does not know what it actua 273 because the driver does not know what it actually gets. For example if we
274 have a device like below:: 274 have a device like below::
275 275
276 Device (BTH) 276 Device (BTH)
277 { 277 {
278 Name (_HID, ...) 278 Name (_HID, ...)
279 279
280 Name (_CRS, ResourceTemplate () { 280 Name (_CRS, ResourceTemplate () {
281 GpioIo (Exclusive, PullNone, 0, 0, I 281 GpioIo (Exclusive, PullNone, 0, 0, IoRestrictionNone,
282 "\\_SB.GPO0", 0, ResourceCon 282 "\\_SB.GPO0", 0, ResourceConsumer) { 15 }
283 GpioIo (Exclusive, PullNone, 0, 0, I 283 GpioIo (Exclusive, PullNone, 0, 0, IoRestrictionNone,
284 "\\_SB.GPO0", 0, ResourceCon 284 "\\_SB.GPO0", 0, ResourceConsumer) { 27 }
285 }) 285 })
286 } 286 }
287 287
288 The driver might expect to get the right GPIO 288 The driver might expect to get the right GPIO when it does::
289 289
290 desc = gpiod_get(dev, "reset", GPIOD_OUT_LOW 290 desc = gpiod_get(dev, "reset", GPIOD_OUT_LOW);
291 if (IS_ERR(desc)) 291 if (IS_ERR(desc))
292 ...error handling... 292 ...error handling...
293 293
294 but since there is no way to know the mapping 294 but since there is no way to know the mapping between "reset" and
295 the GpioIo() in _CRS desc will hold ERR_PTR(-E 295 the GpioIo() in _CRS desc will hold ERR_PTR(-ENOENT).
296 296
297 The driver author can solve this by passing th 297 The driver author can solve this by passing the mapping explicitly
298 (this is the recommended way and it's document 298 (this is the recommended way and it's documented in the above chapter).
299 299
300 The ACPI GPIO mapping tables should not contam 300 The ACPI GPIO mapping tables should not contaminate drivers that are not
301 knowing about which exact device they are serv 301 knowing about which exact device they are servicing on. It implies that
302 the ACPI GPIO mapping tables are hardly linked 302 the ACPI GPIO mapping tables are hardly linked to an ACPI ID and certain
303 objects, as listed in the above chapter, of th 303 objects, as listed in the above chapter, of the device in question.
304 304
305 Getting GPIO descriptor 305 Getting GPIO descriptor
306 ======================= 306 =======================
307 307
308 There are two main approaches to get GPIO reso 308 There are two main approaches to get GPIO resource from ACPI::
309 309
310 desc = gpiod_get(dev, connection_id, flags); 310 desc = gpiod_get(dev, connection_id, flags);
311 desc = gpiod_get_index(dev, connection_id, i 311 desc = gpiod_get_index(dev, connection_id, index, flags);
312 312
313 We may consider two different cases here, i.e. 313 We may consider two different cases here, i.e. when connection ID is
314 provided and otherwise. 314 provided and otherwise.
315 315
316 Case 1:: 316 Case 1::
317 317
318 desc = gpiod_get(dev, "non-null-connection-i 318 desc = gpiod_get(dev, "non-null-connection-id", flags);
319 desc = gpiod_get_index(dev, "non-null-connec 319 desc = gpiod_get_index(dev, "non-null-connection-id", index, flags);
320 320
321 Case 2:: 321 Case 2::
322 322
323 desc = gpiod_get(dev, NULL, flags); 323 desc = gpiod_get(dev, NULL, flags);
324 desc = gpiod_get_index(dev, NULL, index, fla 324 desc = gpiod_get_index(dev, NULL, index, flags);
325 325
326 Case 1 assumes that corresponding ACPI device 326 Case 1 assumes that corresponding ACPI device description must have
327 defined device properties and will prevent to 327 defined device properties and will prevent to getting any GPIO resources
328 otherwise. 328 otherwise.
329 329
330 Case 2 explicitly tells GPIO core to look for 330 Case 2 explicitly tells GPIO core to look for resources in _CRS.
331 331
332 Be aware that gpiod_get_index() in cases 1 and 332 Be aware that gpiod_get_index() in cases 1 and 2, assuming that there
333 are two versions of ACPI device description pr 333 are two versions of ACPI device description provided and no mapping is
334 present in the driver, will return different r 334 present in the driver, will return different resources. That's why a
335 certain driver has to handle them carefully as 335 certain driver has to handle them carefully as explained in the previous
336 chapter. 336 chapter.
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