224 lines
8.0 KiB
Plaintext
224 lines
8.0 KiB
Plaintext
|
_DSD Device Properties Related to GPIO
|
||
|
|
--------------------------------------
|
||
|
|
|
||
|
|
With the release of ACPI 5.1, the _DSD configuration object finally
|
||
|
|
allows names to be given to GPIOs (and other things as well) returned
|
||
|
|
by _CRS. Previously, we were only able to use an integer index to find
|
||
|
|
the corresponding GPIO, which is pretty error prone (it depends on
|
||
|
|
the _CRS output ordering, for example).
|
||
|
|
|
||
|
|
With _DSD we can now query GPIOs using a name instead of an integer
|
||
|
|
index, like the ASL example below shows:
|
||
|
|
|
||
|
|
// Bluetooth device with reset and shutdown GPIOs
|
||
|
|
Device (BTH)
|
||
|
|
{
|
||
|
|
Name (_HID, ...)
|
||
|
|
|
||
|
|
Name (_CRS, ResourceTemplate ()
|
||
|
|
{
|
||
|
|
GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
|
||
|
|
"\\_SB.GPO0", 0, ResourceConsumer) {15}
|
||
|
|
GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
|
||
|
|
"\\_SB.GPO0", 0, ResourceConsumer) {27, 31}
|
||
|
|
})
|
||
|
|
|
||
|
|
Name (_DSD, Package ()
|
||
|
|
{
|
||
|
|
ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
|
||
|
|
Package ()
|
||
|
|
{
|
||
|
|
Package () {"reset-gpios", Package() {^BTH, 1, 1, 0 }},
|
||
|
|
Package () {"shutdown-gpios", Package() {^BTH, 0, 0, 0 }},
|
||
|
|
}
|
||
|
|
})
|
||
|
|
}
|
||
|
|
|
||
|
|
The format of the supported GPIO property is:
|
||
|
|
|
||
|
|
Package () { "name", Package () { ref, index, pin, active_low }}
|
||
|
|
|
||
|
|
ref - The device that has _CRS containing GpioIo()/GpioInt() resources,
|
||
|
|
typically this is the device itself (BTH in our case).
|
||
|
|
index - Index of the GpioIo()/GpioInt() resource in _CRS starting from zero.
|
||
|
|
pin - Pin in the GpioIo()/GpioInt() resource. Typically this is zero.
|
||
|
|
active_low - If 1 the GPIO is marked as active_low.
|
||
|
|
|
||
|
|
Since ACPI GpioIo() resource does not have a field saying whether it is
|
||
|
|
active low or high, the "active_low" argument can be used here. Setting
|
||
|
|
it to 1 marks the GPIO as active low.
|
||
|
|
|
||
|
|
In our Bluetooth example the "reset-gpios" refers to the second GpioIo()
|
||
|
|
resource, second pin in that resource with the GPIO number of 31.
|
||
|
|
|
||
|
|
It is possible to leave holes in the array of GPIOs. This is useful in
|
||
|
|
cases like with SPI host controllers where some chip selects may be
|
||
|
|
implemented as GPIOs and some as native signals. For example a SPI host
|
||
|
|
controller can have chip selects 0 and 2 implemented as GPIOs and 1 as
|
||
|
|
native:
|
||
|
|
|
||
|
|
Package () {
|
||
|
|
"cs-gpios",
|
||
|
|
Package () {
|
||
|
|
^GPIO, 19, 0, 0, // chip select 0: GPIO
|
||
|
|
0, // chip select 1: native signal
|
||
|
|
^GPIO, 20, 0, 0, // chip select 2: GPIO
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
Other supported properties
|
||
|
|
--------------------------
|
||
|
|
|
||
|
|
Following Device Tree compatible device properties are also supported by
|
||
|
|
_DSD device properties for GPIO controllers:
|
||
|
|
|
||
|
|
- gpio-hog
|
||
|
|
- output-high
|
||
|
|
- output-low
|
||
|
|
- input
|
||
|
|
- line-name
|
||
|
|
|
||
|
|
Example:
|
||
|
|
|
||
|
|
Name (_DSD, Package () {
|
||
|
|
// _DSD Hierarchical Properties Extension UUID
|
||
|
|
ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
|
||
|
|
Package () {
|
||
|
|
Package () {"hog-gpio8", "G8PU"}
|
||
|
|
}
|
||
|
|
})
|
||
|
|
|
||
|
|
Name (G8PU, Package () {
|
||
|
|
ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
|
||
|
|
Package () {
|
||
|
|
Package () {"gpio-hog", 1},
|
||
|
|
Package () {"gpios", Package () {8, 0}},
|
||
|
|
Package () {"output-high", 1},
|
||
|
|
Package () {"line-name", "gpio8-pullup"},
|
||
|
|
}
|
||
|
|
})
|
||
|
|
|
||
|
|
- gpio-line-names
|
||
|
|
|
||
|
|
Example:
|
||
|
|
|
||
|
|
Package () {
|
||
|
|
"gpio-line-names",
|
||
|
|
Package () {
|
||
|
|
"SPI0_CS_N", "EXP2_INT", "MUX6_IO", "UART0_RXD", "MUX7_IO",
|
||
|
|
"LVL_C_A1", "MUX0_IO", "SPI1_MISO"
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
See Documentation/devicetree/bindings/gpio/gpio.txt for more information
|
||
|
|
about these properties.
|
||
|
|
|
||
|
|
ACPI GPIO Mappings Provided by Drivers
|
||
|
|
--------------------------------------
|
||
|
|
|
||
|
|
There are systems in which the ACPI tables do not contain _DSD but provide _CRS
|
||
|
|
with GpioIo()/GpioInt() resources and device drivers still need to work with
|
||
|
|
them.
|
||
|
|
|
||
|
|
In those cases ACPI device identification objects, _HID, _CID, _CLS, _SUB, _HRV,
|
||
|
|
available to the driver can be used to identify the device and that is supposed
|
||
|
|
to be sufficient to determine the meaning and purpose of all of the GPIO lines
|
||
|
|
listed by the GpioIo()/GpioInt() resources returned by _CRS. In other words,
|
||
|
|
the driver is supposed to know what to use the GpioIo()/GpioInt() resources for
|
||
|
|
once it has identified the device. Having done that, it can simply assign names
|
||
|
|
to the GPIO lines it is going to use and provide the GPIO subsystem with a
|
||
|
|
mapping between those names and the ACPI GPIO resources corresponding to them.
|
||
|
|
|
||
|
|
To do that, the driver needs to define a mapping table as a NULL-terminated
|
||
|
|
array of struct acpi_gpio_mapping objects that each contain a name, a pointer
|
||
|
|
to an array of line data (struct acpi_gpio_params) objects and the size of that
|
||
|
|
array. Each struct acpi_gpio_params object consists of three fields,
|
||
|
|
crs_entry_index, line_index, active_low, representing the index of the target
|
||
|
|
GpioIo()/GpioInt() resource in _CRS starting from zero, the index of the target
|
||
|
|
line in that resource starting from zero, and the active-low flag for that line,
|
||
|
|
respectively, in analogy with the _DSD GPIO property format specified above.
|
||
|
|
|
||
|
|
For the example Bluetooth device discussed previously the data structures in
|
||
|
|
question would look like this:
|
||
|
|
|
||
|
|
static const struct acpi_gpio_params reset_gpio = { 1, 1, false };
|
||
|
|
static const struct acpi_gpio_params shutdown_gpio = { 0, 0, false };
|
||
|
|
|
||
|
|
static const struct acpi_gpio_mapping bluetooth_acpi_gpios[] = {
|
||
|
|
{ "reset-gpios", &reset_gpio, 1 },
|
||
|
|
{ "shutdown-gpios", &shutdown_gpio, 1 },
|
||
|
|
{ },
|
||
|
|
};
|
||
|
|
|
||
|
|
Next, the mapping table needs to be passed as the second argument to
|
||
|
|
acpi_dev_add_driver_gpios() that will register it with the ACPI device object
|
||
|
|
pointed to by its first argument. That should be done in the driver's .probe()
|
||
|
|
routine. On removal, the driver should unregister its GPIO mapping table by
|
||
|
|
calling acpi_dev_remove_driver_gpios() on the ACPI device object where that
|
||
|
|
table was previously registered.
|
||
|
|
|
||
|
|
Using the _CRS fallback
|
||
|
|
-----------------------
|
||
|
|
|
||
|
|
If a device does not have _DSD or the driver does not create ACPI GPIO
|
||
|
|
mapping, the Linux GPIO framework refuses to return any GPIOs. This is
|
||
|
|
because the driver does not know what it actually gets. For example if we
|
||
|
|
have a device like below:
|
||
|
|
|
||
|
|
Device (BTH)
|
||
|
|
{
|
||
|
|
Name (_HID, ...)
|
||
|
|
|
||
|
|
Name (_CRS, ResourceTemplate () {
|
||
|
|
GpioIo (Exclusive, PullNone, 0, 0, IoRestrictionNone,
|
||
|
|
"\\_SB.GPO0", 0, ResourceConsumer) {15}
|
||
|
|
GpioIo (Exclusive, PullNone, 0, 0, IoRestrictionNone,
|
||
|
|
"\\_SB.GPO0", 0, ResourceConsumer) {27}
|
||
|
|
})
|
||
|
|
}
|
||
|
|
|
||
|
|
The driver might expect to get the right GPIO when it does:
|
||
|
|
|
||
|
|
desc = gpiod_get(dev, "reset", GPIOD_OUT_LOW);
|
||
|
|
|
||
|
|
but since there is no way to know the mapping between "reset" and
|
||
|
|
the GpioIo() in _CRS desc will hold ERR_PTR(-ENOENT).
|
||
|
|
|
||
|
|
The driver author can solve this by passing the mapping explictly
|
||
|
|
(the recommended way and documented in the above chapter).
|
||
|
|
|
||
|
|
The ACPI GPIO mapping tables should not contaminate drivers that are not
|
||
|
|
knowing about which exact device they are servicing on. It implies that
|
||
|
|
the ACPI GPIO mapping tables are hardly linked to ACPI ID and certain
|
||
|
|
objects, as listed in the above chapter, of the device in question.
|
||
|
|
|
||
|
|
Getting GPIO descriptor
|
||
|
|
-----------------------
|
||
|
|
|
||
|
|
There are two main approaches to get GPIO resource from ACPI:
|
||
|
|
desc = gpiod_get(dev, connection_id, flags);
|
||
|
|
desc = gpiod_get_index(dev, connection_id, index, flags);
|
||
|
|
|
||
|
|
We may consider two different cases here, i.e. when connection ID is
|
||
|
|
provided and otherwise.
|
||
|
|
|
||
|
|
Case 1:
|
||
|
|
desc = gpiod_get(dev, "non-null-connection-id", flags);
|
||
|
|
desc = gpiod_get_index(dev, "non-null-connection-id", index, flags);
|
||
|
|
|
||
|
|
Case 2:
|
||
|
|
desc = gpiod_get(dev, NULL, flags);
|
||
|
|
desc = gpiod_get_index(dev, NULL, index, flags);
|
||
|
|
|
||
|
|
Case 1 assumes that corresponding ACPI device description must have
|
||
|
|
defined device properties and will prevent to getting any GPIO resources
|
||
|
|
otherwise.
|
||
|
|
|
||
|
|
Case 2 explicitly tells GPIO core to look for resources in _CRS.
|
||
|
|
|
||
|
|
Be aware that gpiod_get_index() in cases 1 and 2, assuming that there
|
||
|
|
are two versions of ACPI device description provided and no mapping is
|
||
|
|
present in the driver, will return different resources. That's why a
|
||
|
|
certain driver has to handle them carefully as explained in previous
|
||
|
|
chapter.
|