On 05/16/2012 11:22 AM, Jassi Brar wrote:

[...]

OK, my guts feel people might be interested in what's cooking on
my side. I started with the binding text first and then would write
code based upon that approach.

The following might be tweaked as I look deeper into client and DMAC
drivers while deciding upon what the helper functions should be optimally...

-------------------- 8< --------------------


Generic binding to provide a way to provide the client-channel map and
other dmac specific parameters to the dma controller driver

DMA Model:-
  Only the most common characteristics of a dma setup are assumed
in this binding.
Client: Some h/w controller that could request a DMA controller in
the system to perform data transfer on its behalf. Example SPI, MMC,
I2S etc.
DMAC: A DMA Controller instance. Example, PL330, PL08X, SDMA etc.

 The assumed model of the DMAC, in this binding, has P peripheral
interfaces (P request signals) that could request a data transfer
and C physical channels that actually do the data transfers, hence,
at most C out of P peripherals could be served by the DMAC at any
point of time. Usually C := P, but not always. Usually, any of the
physical channels could be employed by the DMAC driver to serve any
client.
 The DMAC driver identifies a client by its i/f number, 'peri_id'
on the given DMAC. For example, TX for SPI has 7th while RX_TX
(half-duplex) for MMC has 10th peripheral interface (request-signal)
on a given DMAC. Usually, any of the physical channels could be
employed by the DMAC driver to serve a client.

* DMA Controller

Required property:

	- #map-cells: Number of elements in each chan-map entry.
		At least 3 elements are required by this binding.

	- chan-map: List of entries that specify clients' 'peri_id'.
		and also possibly DMAC specific per-client data.
		The first element of each entry being the client's
		phandle. The second the direction of data transfer
		w.r.t the client 1 for RX, 2 for TX and  3 for RX|TX.
		The third the 'peri_id' of the client's request signal
		on the DMAC.

Optional properties:

	- #dma-peri-ifs: P, usually the DMAC driver would simply assume the
		number of entries in the 'chan-map' property to be the
		effective number of peripheral request interfaces on the
		DMAC. If specified, it should be at least the number of
		entries in the 'chan-map' property.

	- #dma-channels: C, if specified, it should neither be more than
		the value of 'dma-peri-ifs' nor equal to zero.
		If unspecified,	it is assumed to be equal to the value of
		'dma-peri-ifs', i.e, C := P

	- #private-data: Peculiarities of the DMAC setup, not taken into
		account by this generic model. The decoding of it would
		be private to the DMAC's driver. For ex, some DMAC drivers
		for dmaengine would specify dma_cap_mask_t for the DMAC,
		if they don't need to specify it on a per-client basis
		(i.e, via 4th element of a 'chan-map' entry).

Example:

	dma-controller at 0 {
		compatible = "foo,dmac-xxx";
		#private-data = <0x80808080>;
		#dma-peri-ifs = <32>;
		#dma-channels = <8>;
		#map-cells = <3>;
		chan-map =
			<&i2s1 1 2>,     /* peri_id of I2S's RX is 2 */
			<&i2s1 2 3>,     /* peri_id of I2S's TX is 3 */
			<&mmc1 3 5>,  /* peri_id of MMC's RX_TX is 5 */
			<&spi1 1 6>,
			<&spi1 2 8>,
			...;
	};


* Client Controller

Required property: None.
	The client's DT node doesn't need any DMA specifier.
	Typically it would only comment about the data transfer
	direction associated with each of its request signal.
	Preferably also mentioned in the binding.

Optional property: None.

May be I am still missing something here, but in the case where a client
can use one of two dma controllers, how do you specify which to use? Who
decides?

I was under the impression that you would use the phandle of the dma
controller to specify which controller is used in the client node.

For example ...

 	i2s1: i2s at 70002800 {
 	/* This controller has a request-signal for TX and RX each
 	 * i.e, the driver is going to request a channel for RX(1)
 	 * and another for TX(2).
 	 */
		dma = <dma-controller0>
 		...
 	};

Cheers
Jon