diff options
Diffstat (limited to 'Documentation/acpi')
| -rw-r--r-- | Documentation/acpi/enumeration.txt | 109 |
1 files changed, 108 insertions, 1 deletions
diff --git a/Documentation/acpi/enumeration.txt b/Documentation/acpi/enumeration.txt index 94a65613188..d9be7a97dff 100644 --- a/Documentation/acpi/enumeration.txt +++ b/Documentation/acpi/enumeration.txt @@ -66,6 +66,83 @@ 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. @@ -199,6 +276,8 @@ 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,,) @@ -206,10 +285,20 @@ 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" @@ -220,6 +309,24 @@ 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. +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. |