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