For most platforms, both the _LID method and the lid notifications are
reliable. However, there are exceptions. In order to work with these
-exceptional buggy platforms, special restrictions and expections should be
+exceptional buggy platforms, special restrictions and exceptions should be
taken into account. This document describes the restrictions and the
-expections of the Linux ACPI lid device driver.
+exceptions of the Linux ACPI lid device driver.
Restrictions of the returning value of the _LID control method
trigger some system power saving operations on Windows. Since it is fully
tested, it is reliable from all AML tables.
-Expections for the userspace users of the ACPI lid device driver
+Exceptions for the userspace users of the ACPI lid device driver
================================================================
The ACPI button driver exports the lid state to the userspace via the
C. button.lid_init_state=ignore:
When this option is specified, the ACPI button driver never reports the
initial lid state and there is a compensation mechanism implemented to
- ensure that the reliable "closed" notifications can always be delievered
+ ensure that the reliable "closed" notifications can always be delivered
to the userspace by always pairing "closed" input events with complement
"opened" input events. But there is still no guarantee that the "opened"
notifications can be delivered to the userspace when the lid is actually
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}
})
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
it to 1 marks the GPIO as active low.
+Note, active_low in _DSD does not make sense for GpioInt() resource and
+must be 0. GpioInt() resource has its own means of defining it.
+
In our Bluetooth example the "reset-gpios" refers to the second GpioIo()
resource, second pin in that resource with the GPIO number of 31.
+The GpioIo() resource unfortunately doesn't explicitly provide an initial
+state of the output pin which driver should use during its initialization.
+
+Linux tries to use common sense here and derives the state from the bias
+and polarity settings. The table below shows the expectations:
+
+========= ============= ==============
+Pull Bias Polarity Requested...
+========= ============= ==============
+Implicit x AS IS (assumed firmware configured for us)
+Explicit x (no _DSD) as Pull Bias (Up == High, Down == Low),
+ assuming non-active (Polarity = !Pull Bias)
+Down Low as low, assuming active
+Down High as low, assuming non-active
+Up Low as high, assuming non-active
+Up High as high, assuming active
+========= ============= ==============
+
+That said, for our above example the both GPIOs, since the bias setting
+is explicit and _DSD is present, will be treated as active with a high
+polarity and Linux will configure the pins in this state until a driver
+reprograms them differently.
+
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
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",
}
}
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
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.
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
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.
projects / linux-2.6-microblaze.git / commitdiff