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Documentation: firmware-guide: gpio-properties: Fix factual mistakes

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Fix factual mistakes and style issues in GPIO properties document.
This converts IoRestriction from InputOnly to OutputOnly as pins
in the example are used as outputs.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Andy Shevchenko 2020-10-29 21:32:41 +02:00 committed by Rafael J. Wysocki
parent f8394f232b
commit 1bd3387979
1 changed files with 15 additions and 14 deletions
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29
Documentation/firmware-guide/acpi/gpio-properties.rst
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@ -20,9 +20,9 @@ index, like the ASL example below shows::
Name (_CRS, ResourceTemplate ()
{
GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly,
"\\_SB.GPO0", 0, ResourceConsumer) {15}
GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly,
"\\_SB.GPO0", 0, ResourceConsumer) {27, 31}
})
@ -49,7 +49,7 @@ index
pin
Pin in the GpioIo()/GpioInt() resource. Typically this is zero.
active_low
If 1 the GPIO is marked as 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
@ -112,8 +112,8 @@ Example::
Package () {
"gpio-line-names",
Package () {
"SPI0_CS_N", "EXP2_INT", "MUX6_IO", "UART0_RXD", "MUX7_IO",
"LVL_C_A1", "MUX0_IO", "SPI1_MISO"
"SPI0_CS_N", "EXP2_INT", "MUX6_IO", "UART0_RXD",
"MUX7_IO", "LVL_C_A1", "MUX0_IO", "SPI1_MISO",
}
}
@ -137,7 +137,7 @@ 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
array of struct acpi_gpio_mapping objects that each contains 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
@ -154,13 +154,14 @@ question would look like this::
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
acpi_dev_add_driver_gpios() or its managed analogue 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.
@ -191,12 +192,12 @@ The driver might expect to get the right GPIO when it does::
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 driver author can solve this by passing the mapping explicitly
(this is the recommended way and it's 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
the ACPI GPIO mapping tables are hardly linked to an ACPI ID and certain
objects, as listed in the above chapter, of the device in question.
Getting GPIO descriptor
@ -229,5 +230,5 @@ 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
certain driver has to handle them carefully as explained in the previous
chapter.