[PATCH V3 1/2] of: Add generic device tree DMA helpers

[Jassi Brar]

On 18 May 2012 01:02, Stephen Warren <swarren at wwwdotorg.org> wrote:
>
> Now, the DMA node for an on-SoC DMAC would be in soc.dtsi. Typically,
> the DMAC is connected to many on-SoC devices, and hence soc.dtsi would
> need to specify the routing information for all those devices to avoid
> duplicating it in every board.dts. Now, if you have some DMA requests
> that go off-SoC, the board.dts file might want to add to the routing
> table to indicate what clients connect to those DMA requests. However,
> there's no way in the device tree compiler right now to add to a
> property; you can only completely replace it. That would entail
> duplicating the entire routing information from soc.dtsi into each
> board.dts that wanted to add to it - a bad situation. Splitting the
> routing information into chunks in the client nodes avoids this issue
> entirely.
>
 As already noted by Russell, the dma setup is different than irq or
gpio which deliberately lend to off-SoC attachments. Without fpga'ing,
I find it hard to imagine request-signals going off-SoC.

I only see the issue of different boards sporting a different sub-sets
of clients i.e, a map entry may or may exist for a board but it would
be same for two boards that have it.
 Maybe we could somehow separate out the chan-map and private-data
into board.dts ?
Even if it has to stay in soc.dts, we still have the benefit of having
dmac agnostic client nodes.

cheers!