Messages in this thread | | | Date | Mon, 17 Sep 2012 22:57:53 +0100 | From | Russell King - ARM Linux <> | Subject | Re: [PATCH] dmaengine: add dmanegine slave map api's |
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On Mon, Sep 17, 2012 at 03:20:29PM +0530, Vinod Koul wrote: > On Mon, 2012-09-17 at 09:36 +0100, Russell King - ARM Linux wrote: > > > > I'm not saying take the slave_id out of the map. I'm saying, let the > > > > DMA engine driver itself figure out what dma_chan to return. > > > But wont that assume the dma controller knows which channel to allocate. > > > And how would it know this information? This can be problematic for hard > > > wired muxes, but can be easily done for controller which have > > > programmable mux. > > > > Well, as I have already said, at the moment you're returning the _first_ > > _free_ _channel_ on a DMA device, which almost certainly will always be > > the wrong one. > Yes I overlooked, the continue is wrong. It needs to move to next > available channel. I have fixed it. > > Now on the question if we should allow dmaengine to select channel or > let dma engine driver do that, I don't see how that helps for hard wired > muxes where dma engine driver doesn't know anything of mapping. > > For your OMAP dma this wont matter as I think you have a programmable > mux so you maybe able to use any channel with rightly programmed mux, > right?
Except that we expose one 'channel' per mux setting, so as far as DMA engine goes, the mux number _is_ the channel number - which is the same approach taken by the PL08x and sa11x0 DMA engine drivers. It is the only sane approach to dealing with N hardware channels vs >>N clients.
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