Documentation: firmware-guide: gpio-properties: Fix factual mistakes
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>
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@ -20,9 +20,9 @@ index, like the ASL example below shows::
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Name (_CRS, ResourceTemplate ()
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{
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GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
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GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly,
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"\\_SB.GPO0", 0, ResourceConsumer) {15}
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GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
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GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly,
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"\\_SB.GPO0", 0, ResourceConsumer) {27, 31}
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})
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@ -49,7 +49,7 @@ index
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pin
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Pin in the GpioIo()/GpioInt() resource. Typically this is zero.
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active_low
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If 1 the GPIO is marked as active_low.
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If 1, the GPIO is marked as active_low.
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Since ACPI GpioIo() resource does not have a field saying whether it is
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active low or high, the "active_low" argument can be used here. Setting
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@ -112,8 +112,8 @@ Example::
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Package () {
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"gpio-line-names",
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Package () {
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"SPI0_CS_N", "EXP2_INT", "MUX6_IO", "UART0_RXD", "MUX7_IO",
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"LVL_C_A1", "MUX0_IO", "SPI1_MISO"
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"SPI0_CS_N", "EXP2_INT", "MUX6_IO", "UART0_RXD",
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"MUX7_IO", "LVL_C_A1", "MUX0_IO", "SPI1_MISO",
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}
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}
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@ -137,7 +137,7 @@ to the GPIO lines it is going to use and provide the GPIO subsystem with a
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mapping between those names and the ACPI GPIO resources corresponding to them.
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To do that, the driver needs to define a mapping table as a NULL-terminated
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array of struct acpi_gpio_mapping objects that each contain a name, a pointer
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array of struct acpi_gpio_mapping objects that each contains a name, a pointer
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to an array of line data (struct acpi_gpio_params) objects and the size of that
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array. Each struct acpi_gpio_params object consists of three fields,
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crs_entry_index, line_index, active_low, representing the index of the target
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@ -154,13 +154,14 @@ question would look like this::
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static const struct acpi_gpio_mapping bluetooth_acpi_gpios[] = {
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{ "reset-gpios", &reset_gpio, 1 },
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{ "shutdown-gpios", &shutdown_gpio, 1 },
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{ },
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{ }
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};
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Next, the mapping table needs to be passed as the second argument to
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acpi_dev_add_driver_gpios() that will register it with the ACPI device object
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pointed to by its first argument. That should be done in the driver's .probe()
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routine. On removal, the driver should unregister its GPIO mapping table by
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acpi_dev_add_driver_gpios() or its managed analogue that will
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register it with the ACPI device object pointed to by its first
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argument. That should be done in the driver's .probe() routine.
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On removal, the driver should unregister its GPIO mapping table by
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calling acpi_dev_remove_driver_gpios() on the ACPI device object where that
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table was previously registered.
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@ -191,12 +192,12 @@ The driver might expect to get the right GPIO when it does::
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but since there is no way to know the mapping between "reset" and
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the GpioIo() in _CRS desc will hold ERR_PTR(-ENOENT).
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The driver author can solve this by passing the mapping explictly
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(the recommended way and documented in the above chapter).
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The driver author can solve this by passing the mapping explicitly
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(this is the recommended way and it's documented in the above chapter).
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The ACPI GPIO mapping tables should not contaminate drivers that are not
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knowing about which exact device they are servicing on. It implies that
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the ACPI GPIO mapping tables are hardly linked to ACPI ID and certain
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the ACPI GPIO mapping tables are hardly linked to an ACPI ID and certain
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objects, as listed in the above chapter, of the device in question.
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Getting GPIO descriptor
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@ -229,5 +230,5 @@ Case 2 explicitly tells GPIO core to look for resources in _CRS.
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Be aware that gpiod_get_index() in cases 1 and 2, assuming that there
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are two versions of ACPI device description provided and no mapping is
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present in the driver, will return different resources. That's why a
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certain driver has to handle them carefully as explained in previous
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certain driver has to handle them carefully as explained in the previous
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chapter.
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