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