diff options
Diffstat (limited to 'Documentation/acpi/enumeration.txt')
| -rw-r--r-- | Documentation/acpi/enumeration.txt | 145 |
1 files changed, 116 insertions, 29 deletions
diff --git a/Documentation/acpi/enumeration.txt b/Documentation/acpi/enumeration.txt index 4f27785ca0c..e182be5e3c8 100644 --- a/Documentation/acpi/enumeration.txt +++ b/Documentation/acpi/enumeration.txt @@ -60,11 +60,82 @@ 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/scan.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 ~~~~~~~~~~~~~~~~~~~~~~ @@ -130,7 +201,7 @@ passing those. One idea is to return this in _DSM method like: Return (Local0) } -Then the at25 SPI driver can get this configation by calling _DSM on its +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 }; @@ -151,19 +222,9 @@ ACPI handle like: I2C serial bus support ~~~~~~~~~~~~~~~~~~~~~~ The slaves behind I2C bus controller only need to add the ACPI IDs like -with the platform and SPI drivers. However the I2C bus controller driver -needs to call acpi_i2c_register_devices() after it has added the adapter. - -An I2C bus (controller) driver does: - - ... - ret = i2c_add_numbered_adapter(adapter); - if (ret) - /* handle error */ - - of_i2c_register_devices(adapter); - /* Enumerate the slave devices behind this bus via ACPI */ - acpi_i2c_register_devices(adapter); +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: @@ -185,7 +246,7 @@ input driver: .acpi_match_table ACPI_PTR(mpu3050_acpi_match), }, .probe = mpu3050_probe, - .remove = __devexit_p(mpu3050_remove), + .remove = mpu3050_remove, .id_table = mpu3050_ids, }; @@ -199,6 +260,8 @@ the device to the driver. For example: { Name (SBUF, ResourceTemplate() { + ... + // Used to power on/off the device GpioIo (Exclusive, PullDefault, 0x0000, 0x0000, IoRestrictionOutputOnly, "\\_SB.PCI0.GPI0", 0x00, ResourceConsumer,,) @@ -206,22 +269,46 @@ the device to the driver. For example: // Pin List 0x0055 } + + // Interrupt for the device + GpioInt (Edge, ActiveHigh, ExclusiveAndWake, PullNone, + 0x0000, "\\_SB.PCI0.GPI0", 0x00, ResourceConsumer,,) + { + // Pin list + 0x0058 + } + ... - Return (SBUF) } + + 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. +we need to translate them to the corresponding Linux GPIO descriptors. + +There is a standard GPIO API for that and is documented in +Documentation/gpio/. + +In the above example we can get the corresponding two GPIO descriptors with +a code like this: -The driver can do this by including <linux/acpi_gpio.h> and then calling -acpi_get_gpio(path, gpio). This will return the Linux GPIO number or -negative errno if there was no translation found. + #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 */ -Other GpioIo parameters must be converted first by the driver to be -suitable to the gpiolib before passing them. + /* Now we can use the GPIO descriptors */ -In case of GpioInt resource an additional call to gpio_to_irq() must be -done before calling request_irq(). +There are also devm_* versions of these functions which release the +descriptors once the device is released. |