1.. SPDX-License-Identifier: GPL-2.0 2 3====================================== 4_DSD Device Properties Related to GPIO 5====================================== 6 7With the release of ACPI 5.1, the _DSD configuration object finally 8allows names to be given to GPIOs (and other things as well) returned 9by _CRS. Previously, we were only able to use an integer index to find 10the corresponding GPIO, which is pretty error prone (it depends on 11the _CRS output ordering, for example). 12 13With _DSD we can now query GPIOs using a name instead of an integer 14index, like the ASL example below shows:: 15 16 // Bluetooth device with reset and shutdown GPIOs 17 Device (BTH) 18 { 19 Name (_HID, ...) 20 21 Name (_CRS, ResourceTemplate () 22 { 23 GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly, 24 "\\_SB.GPO0", 0, ResourceConsumer) {15} 25 GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly, 26 "\\_SB.GPO0", 0, ResourceConsumer) {27, 31} 27 }) 28 29 Name (_DSD, Package () 30 { 31 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), 32 Package () 33 { 34 Package () {"reset-gpios", Package() {^BTH, 1, 1, 0 }}, 35 Package () {"shutdown-gpios", Package() {^BTH, 0, 0, 0 }}, 36 } 37 }) 38 } 39 40The format of the supported GPIO property is:: 41 42 Package () { "name", Package () { ref, index, pin, active_low }} 43 44ref 45 The device that has _CRS containing GpioIo()/GpioInt() resources, 46 typically this is the device itself (BTH in our case). 47index 48 Index of the GpioIo()/GpioInt() resource in _CRS starting from zero. 49pin 50 Pin in the GpioIo()/GpioInt() resource. Typically this is zero. 51active_low 52 If 1, the GPIO is marked as active_low. 53 54Since ACPI GpioIo() resource does not have a field saying whether it is 55active low or high, the "active_low" argument can be used here. Setting 56it to 1 marks the GPIO as active low. 57 58Note, active_low in _DSD does not make sense for GpioInt() resource and 59must be 0. GpioInt() resource has its own means of defining it. 60 61In our Bluetooth example the "reset-gpios" refers to the second GpioIo() 62resource, second pin in that resource with the GPIO number of 31. 63 64It is possible to leave holes in the array of GPIOs. This is useful in 65cases like with SPI host controllers where some chip selects may be 66implemented as GPIOs and some as native signals. For example a SPI host 67controller can have chip selects 0 and 2 implemented as GPIOs and 1 as 68native:: 69 70 Package () { 71 "cs-gpios", 72 Package () { 73 ^GPIO, 19, 0, 0, // chip select 0: GPIO 74 0, // chip select 1: native signal 75 ^GPIO, 20, 0, 0, // chip select 2: GPIO 76 } 77 } 78 79Other supported properties 80========================== 81 82Following Device Tree compatible device properties are also supported by 83_DSD device properties for GPIO controllers: 84 85- gpio-hog 86- output-high 87- output-low 88- input 89- line-name 90 91Example:: 92 93 Name (_DSD, Package () { 94 // _DSD Hierarchical Properties Extension UUID 95 ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"), 96 Package () { 97 Package () {"hog-gpio8", "G8PU"} 98 } 99 }) 100 101 Name (G8PU, Package () { 102 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), 103 Package () { 104 Package () {"gpio-hog", 1}, 105 Package () {"gpios", Package () {8, 0}}, 106 Package () {"output-high", 1}, 107 Package () {"line-name", "gpio8-pullup"}, 108 } 109 }) 110 111- gpio-line-names 112 113Example:: 114 115 Package () { 116 "gpio-line-names", 117 Package () { 118 "SPI0_CS_N", "EXP2_INT", "MUX6_IO", "UART0_RXD", 119 "MUX7_IO", "LVL_C_A1", "MUX0_IO", "SPI1_MISO", 120 } 121 } 122 123See Documentation/devicetree/bindings/gpio/gpio.txt for more information 124about these properties. 125 126ACPI GPIO Mappings Provided by Drivers 127====================================== 128 129There are systems in which the ACPI tables do not contain _DSD but provide _CRS 130with GpioIo()/GpioInt() resources and device drivers still need to work with 131them. 132 133In those cases ACPI device identification objects, _HID, _CID, _CLS, _SUB, _HRV, 134available to the driver can be used to identify the device and that is supposed 135to be sufficient to determine the meaning and purpose of all of the GPIO lines 136listed by the GpioIo()/GpioInt() resources returned by _CRS. In other words, 137the driver is supposed to know what to use the GpioIo()/GpioInt() resources for 138once it has identified the device. Having done that, it can simply assign names 139to the GPIO lines it is going to use and provide the GPIO subsystem with a 140mapping between those names and the ACPI GPIO resources corresponding to them. 141 142To do that, the driver needs to define a mapping table as a NULL-terminated 143array of struct acpi_gpio_mapping objects that each contains a name, a pointer 144to an array of line data (struct acpi_gpio_params) objects and the size of that 145array. Each struct acpi_gpio_params object consists of three fields, 146crs_entry_index, line_index, active_low, representing the index of the target 147GpioIo()/GpioInt() resource in _CRS starting from zero, the index of the target 148line in that resource starting from zero, and the active-low flag for that line, 149respectively, in analogy with the _DSD GPIO property format specified above. 150 151For the example Bluetooth device discussed previously the data structures in 152question would look like this:: 153 154 static const struct acpi_gpio_params reset_gpio = { 1, 1, false }; 155 static const struct acpi_gpio_params shutdown_gpio = { 0, 0, false }; 156 157 static const struct acpi_gpio_mapping bluetooth_acpi_gpios[] = { 158 { "reset-gpios", &reset_gpio, 1 }, 159 { "shutdown-gpios", &shutdown_gpio, 1 }, 160 { } 161 }; 162 163Next, the mapping table needs to be passed as the second argument to 164acpi_dev_add_driver_gpios() or its managed analogue that will 165register it with the ACPI device object pointed to by its first 166argument. That should be done in the driver's .probe() routine. 167On removal, the driver should unregister its GPIO mapping table by 168calling acpi_dev_remove_driver_gpios() on the ACPI device object where that 169table was previously registered. 170 171Using the _CRS fallback 172======================= 173 174If a device does not have _DSD or the driver does not create ACPI GPIO 175mapping, the Linux GPIO framework refuses to return any GPIOs. This is 176because the driver does not know what it actually gets. For example if we 177have a device like below:: 178 179 Device (BTH) 180 { 181 Name (_HID, ...) 182 183 Name (_CRS, ResourceTemplate () { 184 GpioIo (Exclusive, PullNone, 0, 0, IoRestrictionNone, 185 "\\_SB.GPO0", 0, ResourceConsumer) {15} 186 GpioIo (Exclusive, PullNone, 0, 0, IoRestrictionNone, 187 "\\_SB.GPO0", 0, ResourceConsumer) {27} 188 }) 189 } 190 191The driver might expect to get the right GPIO when it does:: 192 193 desc = gpiod_get(dev, "reset", GPIOD_OUT_LOW); 194 195but since there is no way to know the mapping between "reset" and 196the GpioIo() in _CRS desc will hold ERR_PTR(-ENOENT). 197 198The driver author can solve this by passing the mapping explicitly 199(this is the recommended way and it's documented in the above chapter). 200 201The ACPI GPIO mapping tables should not contaminate drivers that are not 202knowing about which exact device they are servicing on. It implies that 203the ACPI GPIO mapping tables are hardly linked to an ACPI ID and certain 204objects, as listed in the above chapter, of the device in question. 205 206Getting GPIO descriptor 207======================= 208 209There are two main approaches to get GPIO resource from ACPI:: 210 211 desc = gpiod_get(dev, connection_id, flags); 212 desc = gpiod_get_index(dev, connection_id, index, flags); 213 214We may consider two different cases here, i.e. when connection ID is 215provided and otherwise. 216 217Case 1:: 218 219 desc = gpiod_get(dev, "non-null-connection-id", flags); 220 desc = gpiod_get_index(dev, "non-null-connection-id", index, flags); 221 222Case 2:: 223 224 desc = gpiod_get(dev, NULL, flags); 225 desc = gpiod_get_index(dev, NULL, index, flags); 226 227Case 1 assumes that corresponding ACPI device description must have 228defined device properties and will prevent to getting any GPIO resources 229otherwise. 230 231Case 2 explicitly tells GPIO core to look for resources in _CRS. 232 233Be aware that gpiod_get_index() in cases 1 and 2, assuming that there 234are two versions of ACPI device description provided and no mapping is 235present in the driver, will return different resources. That's why a 236certain driver has to handle them carefully as explained in the previous 237chapter. 238