dma: acpi-dma: introduce ACPI DMA helpers

There is a new generic API to get a DMA channel for a slave device (commit
9a6cecc8 "dmaengine: add helper function to request a slave DMA channel"). In
similar fashion to the DT case (commit aa3da644 "of: Add generic device tree
DMA helpers") we introduce helpers to the DMAC drivers which are enumerated by
ACPI.

The proposed extension provides the following API calls:
	acpi_dma_controller_register(), devm_acpi_dma_controller_register()
	acpi_dma_controller_free(), devm_acpi_dma_controller_free()
	acpi_dma_simple_xlate()
	acpi_dma_request_slave_chan_by_index()
	acpi_dma_request_slave_chan_by_name()

The first two should be used, for example, at probe() and remove() of the
corresponding DMAC driver. At the register stage the DMAC driver supplies a
custom xlate() function to translate a struct dma_spec into struct dma_chan.

Accordingly to the ACPI Fixed DMA resource specification the only two pieces of
information the slave device has are the channel id and the request line (slave
id). Those two are represented by struct dma_spec. The
acpi_dma_request_slave_chan_by_index() provides access to the specifix FixedDMA
resource by its index. Whereas dma_request_slave_channel() takes a string
parameter to identify the DMA resources required by the slave device. To make a
slave device driver work with both DeviceTree and ACPI enumeration a simple
convention is established: "tx" corresponds to the index 0 and "rx" to the
index 1. In case of robust configuration the slave device driver unfortunately
needs to call acpi_dma_request_slave_chan_by_index() directly.

Additionally the patch provides "managed" version of the register/free pair
i.e. devm_acpi_dma_controller_register() and devm_acpi_dma_controller_free().
Usually, the driver uses only devm_acpi_dma_controller_register().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

1 files changed, 77 insertions, 0 deletions

diff --git a/Documentation/acpi/enumeration.txt b/Documentation/acpi/enumeration.txt
index 94a6561..2874c90 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.