On 05/18/2012 02:49 PM, Arnd Bergmann wrote:

On Wednesday 16 May 2012, Stephen Warren wrote:

quoted

Simple case:

/* e.g. FIFO TX DMA req - 2 DMACs possible */
dma-req-0 = <&dmac1 DMAC1_DMA_REQ_6>;
/* e.g. FIFO RX DMA req 1 DMAC possible */
dma-req-1 = <&dmac1 DMAC1_DMA_REQ_8>;

Multiple DMAC case:

/* e.g. FIFO TX DMA req - 2 DMACs possible */
dma-req-0 = <&dmac1 DMAC1_DMA_REQ_6 &dmac2 DMA_2_DMA_REQ_8>;
/* e.g. FIFO RX DMA req 1 DMAC possible */
dma-req-1 = <&dmac1 DMAC1_DMA_REQ_8>;

Then, when the DMA client calls the standard API to "get DMA channel for
my outbound DMA request "n", the core code will kasprintf("dma-req-%d",
n); to generate the property name. That's how pinctrl works.

Does that seem better?

Yes, that is one way that I suggested at an earlier point. After some
discussion, I would use a different syntax for these though, to the exact
same effect, writing it as


	dmas = <&dmac1 DMAC1_DMA_REQ_6>,  <&dmac2 DMA_2_DMA_REQ_8>,  <&dmac1 DMAC1_DMA_REQ_8>;
	dma-names = "tx", "tx", "rx";

That looks pretty reasonable. One comment below.

The driver can still request the dma line by name "tx" and the subsystem
would pick one out of those with the same name.

For the majority of cases, we would only need a single dma request line

Hmm. Many devices have multiple different FIFOs, and hence multiple DMA
request signals (e.g. Tegra I2S has separate RX and TX FIFO, Tegra
S/PDIF has 2 FIFOs in each direction). That would require the driver to
always use get_by_name() to differentiate between 2/4 options for the
same DMA req or 2/4 different DMA requests. Most other bindings allow
use of get_by_id() or get_by_name() interchangeably.

and could leave out the dma-names property, so when you don't ask for a
specific name, you just get any dma line out of the dmas array.

	Arnd