343 lines
9.7 KiB
Plaintext
343 lines
9.7 KiB
Plaintext
ACPI based device enumeration
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
ACPI 5 introduced a set of new resources (UartTSerialBus, I2cSerialBus,
|
|
SpiSerialBus, GpioIo and GpioInt) which can be used in enumerating slave
|
|
devices behind serial bus controllers.
|
|
|
|
In addition we are starting to see peripherals integrated in the
|
|
SoC/Chipset to appear only in ACPI namespace. These are typically devices
|
|
that are accessed through memory-mapped registers.
|
|
|
|
In order to support this and re-use the existing drivers as much as
|
|
possible we decided to do following:
|
|
|
|
o Devices that have no bus connector resource are represented as
|
|
platform devices.
|
|
|
|
o Devices behind real busses where there is a connector resource
|
|
are represented as struct spi_device or struct i2c_device
|
|
(standard UARTs are not busses so there is no struct uart_device).
|
|
|
|
As both ACPI and Device Tree represent a tree of devices (and their
|
|
resources) this implementation follows the Device Tree way as much as
|
|
possible.
|
|
|
|
The ACPI implementation enumerates devices behind busses (platform, SPI and
|
|
I2C), creates the physical devices and binds them to their ACPI handle in
|
|
the ACPI namespace.
|
|
|
|
This means that when ACPI_HANDLE(dev) returns non-NULL the device was
|
|
enumerated from ACPI namespace. This handle can be used to extract other
|
|
device-specific configuration. There is an example of this below.
|
|
|
|
Platform bus support
|
|
~~~~~~~~~~~~~~~~~~~~
|
|
Since we are using platform devices to represent devices that are not
|
|
connected to any physical bus we only need to implement a platform driver
|
|
for the device and add supported ACPI IDs. If this same IP-block is used on
|
|
some other non-ACPI platform, the driver might work out of the box or needs
|
|
some minor changes.
|
|
|
|
Adding ACPI support for an existing driver should be pretty
|
|
straightforward. Here is the simplest example:
|
|
|
|
#ifdef CONFIG_ACPI
|
|
static struct acpi_device_id mydrv_acpi_match[] = {
|
|
/* ACPI IDs here */
|
|
{ }
|
|
};
|
|
MODULE_DEVICE_TABLE(acpi, mydrv_acpi_match);
|
|
#endif
|
|
|
|
static struct platform_driver my_driver = {
|
|
...
|
|
.driver = {
|
|
.acpi_match_table = ACPI_PTR(mydrv_acpi_match),
|
|
},
|
|
};
|
|
|
|
If the driver needs to perform more complex initialization like getting and
|
|
configuring GPIOs it can get its ACPI handle and extract this information
|
|
from ACPI tables.
|
|
|
|
Currently the kernel is not able to automatically determine from which ACPI
|
|
device it should make the corresponding platform device so we need to add
|
|
the ACPI device explicitly to acpi_platform_device_ids list defined in
|
|
drivers/acpi/acpi_platform.c. This limitation is only for the platform
|
|
devices, SPI and I2C devices are created automatically as described below.
|
|
|
|
DMA support
|
|
~~~~~~~~~~~
|
|
DMA controllers enumerated via ACPI should be registered in the system to
|
|
provide generic access to their resources. For example, a driver that would
|
|
like to be accessible to slave devices via generic API call
|
|
dma_request_slave_channel() must register itself at the end of the probe
|
|
function like this:
|
|
|
|
err = devm_acpi_dma_controller_register(dev, xlate_func, dw);
|
|
/* Handle the error if it's not a case of !CONFIG_ACPI */
|
|
|
|
and implement custom xlate function if needed (usually acpi_dma_simple_xlate()
|
|
is enough) which converts the FixedDMA resource provided by struct
|
|
acpi_dma_spec into the corresponding DMA channel. A piece of code for that case
|
|
could look like:
|
|
|
|
#ifdef CONFIG_ACPI
|
|
struct filter_args {
|
|
/* Provide necessary information for the filter_func */
|
|
...
|
|
};
|
|
|
|
static bool filter_func(struct dma_chan *chan, void *param)
|
|
{
|
|
/* Choose the proper channel */
|
|
...
|
|
}
|
|
|
|
static struct dma_chan *xlate_func(struct acpi_dma_spec *dma_spec,
|
|
struct acpi_dma *adma)
|
|
{
|
|
dma_cap_mask_t cap;
|
|
struct filter_args args;
|
|
|
|
/* Prepare arguments for filter_func */
|
|
...
|
|
return dma_request_channel(cap, filter_func, &args);
|
|
}
|
|
#else
|
|
static struct dma_chan *xlate_func(struct acpi_dma_spec *dma_spec,
|
|
struct acpi_dma *adma)
|
|
{
|
|
return NULL;
|
|
}
|
|
#endif
|
|
|
|
dma_request_slave_channel() will call xlate_func() for each registered DMA
|
|
controller. In the xlate function the proper channel must be chosen based on
|
|
information in struct acpi_dma_spec and the properties of the controller
|
|
provided by struct acpi_dma.
|
|
|
|
Clients must call dma_request_slave_channel() with the string parameter that
|
|
corresponds to a specific FixedDMA resource. By default "tx" means the first
|
|
entry of the FixedDMA resource array, "rx" means the second entry. The table
|
|
below shows a layout:
|
|
|
|
Device (I2C0)
|
|
{
|
|
...
|
|
Method (_CRS, 0, NotSerialized)
|
|
{
|
|
Name (DBUF, ResourceTemplate ()
|
|
{
|
|
FixedDMA (0x0018, 0x0004, Width32bit, _Y48)
|
|
FixedDMA (0x0019, 0x0005, Width32bit, )
|
|
})
|
|
...
|
|
}
|
|
}
|
|
|
|
So, the FixedDMA with request line 0x0018 is "tx" and next one is "rx" in
|
|
this example.
|
|
|
|
In robust cases the client unfortunately needs to call
|
|
acpi_dma_request_slave_chan_by_index() directly and therefore choose the
|
|
specific FixedDMA resource by its index.
|
|
|
|
SPI serial bus support
|
|
~~~~~~~~~~~~~~~~~~~~~~
|
|
Slave devices behind SPI bus have SpiSerialBus resource attached to them.
|
|
This is extracted automatically by the SPI core and the slave devices are
|
|
enumerated once spi_register_master() is called by the bus driver.
|
|
|
|
Here is what the ACPI namespace for a SPI slave might look like:
|
|
|
|
Device (EEP0)
|
|
{
|
|
Name (_ADR, 1)
|
|
Name (_CID, Package() {
|
|
"ATML0025",
|
|
"AT25",
|
|
})
|
|
...
|
|
Method (_CRS, 0, NotSerialized)
|
|
{
|
|
SPISerialBus(1, PolarityLow, FourWireMode, 8,
|
|
ControllerInitiated, 1000000, ClockPolarityLow,
|
|
ClockPhaseFirst, "\\_SB.PCI0.SPI1",)
|
|
}
|
|
...
|
|
|
|
The SPI device drivers only need to add ACPI IDs in a similar way than with
|
|
the platform device drivers. Below is an example where we add ACPI support
|
|
to at25 SPI eeprom driver (this is meant for the above ACPI snippet):
|
|
|
|
#ifdef CONFIG_ACPI
|
|
static struct acpi_device_id at25_acpi_match[] = {
|
|
{ "AT25", 0 },
|
|
{ },
|
|
};
|
|
MODULE_DEVICE_TABLE(acpi, at25_acpi_match);
|
|
#endif
|
|
|
|
static struct spi_driver at25_driver = {
|
|
.driver = {
|
|
...
|
|
.acpi_match_table = ACPI_PTR(at25_acpi_match),
|
|
},
|
|
};
|
|
|
|
Note that this driver actually needs more information like page size of the
|
|
eeprom etc. but at the time writing this there is no standard way of
|
|
passing those. One idea is to return this in _DSM method like:
|
|
|
|
Device (EEP0)
|
|
{
|
|
...
|
|
Method (_DSM, 4, NotSerialized)
|
|
{
|
|
Store (Package (6)
|
|
{
|
|
"byte-len", 1024,
|
|
"addr-mode", 2,
|
|
"page-size, 32
|
|
}, Local0)
|
|
|
|
// Check UUIDs etc.
|
|
|
|
Return (Local0)
|
|
}
|
|
|
|
Then the at25 SPI driver can get this configuration by calling _DSM on its
|
|
ACPI handle like:
|
|
|
|
struct acpi_buffer output = { ACPI_ALLOCATE_BUFFER, NULL };
|
|
struct acpi_object_list input;
|
|
acpi_status status;
|
|
|
|
/* Fill in the input buffer */
|
|
|
|
status = acpi_evaluate_object(ACPI_HANDLE(&spi->dev), "_DSM",
|
|
&input, &output);
|
|
if (ACPI_FAILURE(status))
|
|
/* Handle the error */
|
|
|
|
/* Extract the data here */
|
|
|
|
kfree(output.pointer);
|
|
|
|
I2C serial bus support
|
|
~~~~~~~~~~~~~~~~~~~~~~
|
|
The slaves behind I2C bus controller only need to add the ACPI IDs like
|
|
with the platform and SPI drivers. The I2C core automatically enumerates
|
|
any slave devices behind the controller device once the adapter is
|
|
registered.
|
|
|
|
Below is an example of how to add ACPI support to the existing mpu3050
|
|
input driver:
|
|
|
|
#ifdef CONFIG_ACPI
|
|
static struct acpi_device_id mpu3050_acpi_match[] = {
|
|
{ "MPU3050", 0 },
|
|
{ },
|
|
};
|
|
MODULE_DEVICE_TABLE(acpi, mpu3050_acpi_match);
|
|
#endif
|
|
|
|
static struct i2c_driver mpu3050_i2c_driver = {
|
|
.driver = {
|
|
.name = "mpu3050",
|
|
.owner = THIS_MODULE,
|
|
.pm = &mpu3050_pm,
|
|
.of_match_table = mpu3050_of_match,
|
|
.acpi_match_table ACPI_PTR(mpu3050_acpi_match),
|
|
},
|
|
.probe = mpu3050_probe,
|
|
.remove = mpu3050_remove,
|
|
.id_table = mpu3050_ids,
|
|
};
|
|
|
|
GPIO support
|
|
~~~~~~~~~~~~
|
|
ACPI 5 introduced two new resources to describe GPIO connections: GpioIo
|
|
and GpioInt. These resources are used be used to pass GPIO numbers used by
|
|
the device to the driver. For example:
|
|
|
|
Method (_CRS, 0, NotSerialized)
|
|
{
|
|
Name (SBUF, ResourceTemplate()
|
|
{
|
|
...
|
|
// Used to power on/off the device
|
|
GpioIo (Exclusive, PullDefault, 0x0000, 0x0000,
|
|
IoRestrictionOutputOnly, "\\_SB.PCI0.GPI0",
|
|
0x00, ResourceConsumer,,)
|
|
{
|
|
// Pin List
|
|
0x0055
|
|
}
|
|
|
|
// Interrupt for the device
|
|
GpioInt (Edge, ActiveHigh, ExclusiveAndWake, PullNone,
|
|
0x0000, "\\_SB.PCI0.GPI0", 0x00, ResourceConsumer,,)
|
|
{
|
|
// Pin list
|
|
0x0058
|
|
}
|
|
|
|
...
|
|
|
|
}
|
|
|
|
Return (SBUF)
|
|
}
|
|
|
|
These GPIO numbers are controller relative and path "\\_SB.PCI0.GPI0"
|
|
specifies the path to the controller. In order to use these GPIOs in Linux
|
|
we need to translate them to the Linux GPIO numbers.
|
|
|
|
In a simple case of just getting the Linux GPIO number from device
|
|
resources one can use acpi_get_gpio_by_index() helper function. It takes
|
|
pointer to the device and index of the GpioIo/GpioInt descriptor in the
|
|
device resources list. For example:
|
|
|
|
int gpio_irq, gpio_power;
|
|
int ret;
|
|
|
|
gpio_irq = acpi_get_gpio_by_index(dev, 1, NULL);
|
|
if (gpio_irq < 0)
|
|
/* handle error */
|
|
|
|
gpio_power = acpi_get_gpio_by_index(dev, 0, NULL);
|
|
if (gpio_power < 0)
|
|
/* handle error */
|
|
|
|
/* Now we can use the GPIO numbers */
|
|
|
|
Other GpioIo parameters must be converted first by the driver to be
|
|
suitable to the gpiolib before passing them.
|
|
|
|
In case of GpioInt resource an additional call to gpio_to_irq() must be
|
|
done before calling request_irq().
|
|
|
|
Note that the above API is ACPI specific and not recommended for drivers
|
|
that need to support non-ACPI systems. The recommended way is to use
|
|
the descriptor based GPIO interfaces. The above example looks like this
|
|
when converted to the GPIO desc:
|
|
|
|
#include <linux/gpio/consumer.h>
|
|
...
|
|
|
|
struct gpio_desc *irq_desc, *power_desc;
|
|
|
|
irq_desc = gpiod_get_index(dev, NULL, 1);
|
|
if (IS_ERR(irq_desc))
|
|
/* handle error */
|
|
|
|
power_desc = gpiod_get_index(dev, NULL, 0);
|
|
if (IS_ERR(power_desc))
|
|
/* handle error */
|
|
|
|
/* Now we can use the GPIO descriptors */
|
|
|
|
See also Documentation/gpio.txt.
|