On Thu, Dec 11, 2014 at 09:47:29AM +0200, Laurent Pinchart wrote: > On Thursday 11 December 2014 08:37:27 Wolfram Sang wrote: > > > I think this is a limitation of driver may not be for HW. The right model > > > for dma_chan is to be viewed as SW channels and not the ones of HW (yes > > > that is how most of the drivers use that, but we can improve upon) > > > > > > If we rework the driver to view dma_chan as SW channels, then you can > > > accept multiple channel requests and accept based on if we are able link > > > the channel to that peripheral or not. > > > > In my understanding, the DMA driver does exactly that. > > Actually it doesn't at the moment, I should implement that. OK, so I was misinterpreting the overcommitment. Thanks for the correction! > > However, it is not even loaded at the time the I2C driver wants a channel, > > so the dmaengine core defers the probe. That is the problem for optional DMA > > channels: we can't know when deferring probe won't help anymore and don't > > know when it is time to fall back to PIO. > > This is true regardless of the whether the driver exposes HW or SW channels. Yup.
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