of: Add generic device tree DMA helpers

This is based upon the work by Benoit Cousson [1] and Nicolas Ferre [2]
to add some basic helpers to retrieve a DMA controller device_node and the
DMA request/channel information.

Aim of DMA helpers
- The purpose of device-tree (as far as I understand), is to describe the
  capabilites of the hardware. Thinking about DMA controllers purely from the
  context of the hardware to begin with, we can describe a device in terms of
  a DMA controller as follows ...
  	1. Number of DMA controllers
	2. Number of channels (maybe physical or logical)
	3. Mapping of DMA requests signals to DMA controller
	4. Number of DMA interrupts
	5. Mapping of DMA interrupts to channels
- With the above in mind the aim of the DT DMA helper functions is to extract
  the above information from the DT and provide to the appropriate driver.
  However, due to the vast number of DMA controllers and not all are using a
  common driver (such as DMA Engine) it has been seen that this is not a
  trivial task. In previous discussions on this topic the following concerns
  have been raised ...
	1. How does the binding identify when there are multiple DMA
	   controllers?
  	2. How to support both legacy DMA controllers not using DMA Engine as
	   well as those that support DMA Engine.
	3. When using with DMA Engine how do we support the various
	   implementations where the opaque filter function parameter differs
	   between implementations?
	4. How do we handle DMA channels that are identified with a string
	   versus a integer?
- Hence the design of the DMA helpers has to accomodate the above or align on
  an agreement what can be or should be supported.

Design of DMA helpers

1. Supporting devices with multiple DMA controllers

   In the case of DMA controllers that are using DMA Engine, requesting a
   channel is performed by calling the following function.

	struct dma_chan *dma_request_channel(dma_cap_mask_t mask,
			dma_filter_fn filter_fn,
			void *filter_param);

   The mask variable is used to identify the device controller in a list of
   controllers. The filter_fn and filter_param are used to identify the
   required dma channel and return a handle to the dma channel of type
   dma_chan. From the examples I have seen, the mask and filter_fn are constant
   for a given DMA controller. Therefore, when registering a DMA controller with
   device tree we can pass these parameters using the below structure and store
   them so that a device can use them when requesting a channel.

	struct of_dma_filter_info {
		dma_cap_mask_t  dma_cap;
		dma_filter_fn   filter_fn;
	};

   The filter_param variable shown in the above function is of an unknown type
   and is typically specific to the DMA engine implementation for a given DMA
   controller. To allow some flexibility in the type and formating of this
   filter_param we employ an xlate to translate the device-tree binding
   information into the appropriate format. The xlate function used for a DMA
   controller is specified when registering the DMA controller.

   Based upon the above, our register function for the DMA controller now looks
   like below, where the data variable can be used to pass a pointer to the
   of_dma_filter_info structure shown above. It is declared as a void * pointer
   to allow other data structures to be passed as well.

	int of_dma_controller_register(struct device_node *np,
		struct dma_chan *(*of_dma_xlate)
		(struct of_phandle_args *, struct of_dma *),
		void *data)

2. Representing and requesting channel information

   Please see the dma binding documentation included in this patch for a
   description of how DMA controllers and channel information should be
   represented with device-tree. For more information on how this binding
   came about please see [3].

   A driver can request the DMA channel information by calling the following
   function, where name is an optional parameter and flags is a required
   parameter used for identifying a DMA channel. Flags may be controller
   specific or it may simply specify is a DMA channel is used for read or
   write. See the binding document for some examples for how name and flags
   are used. This function has been designed to return a structure of type
   dma_chan to work with the DMA engine driver.

	struct dma_chan *of_dma_request_channel(struct device_node *np,
						char *name, int flags)

3. Supporting legacy devices not using DMA Engine

   These devices present a problem, as there may not be a uniform way to easily
   support them with regard to device tree. Ideally, these should be migrated
   to DMA engine. However, if this is not possible, then they should still be
   able to use this binding, the only constaint imposed by this implementation
   is that when requesting a DMA channel via of_dma_request_channel(), it will
   return a type of dma_chan.

This implementation has been tested on OMAP4460 using the kernel v3.6-rc2. I
have validated that MMC is working on the PANDA board with this implementation.

v4: - revert the removal of xlate function from v3
    - update the proposed binding format and APIs based upon discussions [3]
v3: - avoid passing an xlate function and instead pass DMA engine parameters
    - define number of dma channels and requests in dma-controller node
v2: - remove of_dma_to_resource API
    - make property #dma-cells required (no fallback anymore)
    - another check in of_dma_xlate_onenumbercell() function

[1] http://article.gmane.org/gmane.linux.drivers.devicetree/12022
[2] http://article.gmane.org/gmane.linux.ports.arm.omap/73622
[3] http://marc.info/?l=linux-omap&m=133582085008539&w=2

Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Benoit Cousson <b-cousson@ti.com>
Cc: Stephen Warren <swarren@nvidia.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jon Hunter <jon-hunter@ti.com>

crap
arm/dts: OMAP4: Add SDMA controller binding

Add SDMA controller binding for OMAP4 devices and populate DMA client
information for devices using DMA.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
dmaengine: add helper function to request a slave DMA channel

Currently slave DMA channels are requested by calling dma_request_channel()
and requires DMA clients to pass various filter parameters to obtain the
appropriate channel.

With device-tree being used to by architectures such as arm and the addition
of device-tree helper functions to extract the relevant slave DMA channel
information for device-tree, add a new function to slave DMA channel from
device-tree using a name and/or flags variable to identify a channel. This
function is currently a simple wrapper that calls the device-tree
of_dma_request_slave_channel() function.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
dmaengine: OMAP: Register SDMA controller with Device Tree DMA driver

If the device-tree blob is present during boot, then register the SDMA
controller with the device-tree DMA driver so that we can use device-tree
to look-up DMA client information.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
mmc: omap_hsmmc: Use device-tree to look-up DMA information

If the device-tree blob is present during boot, then use device-tree to
look-up the MMC hosts DMA information.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>