On Fri, Dec 09, 2016 at 06:34:15PM +0100, Mason wrote: > On 09/12/2016 18:17, Vinod Koul wrote: > > > On Fri, Dec 09, 2016 at 11:25:57AM +0100, Sebastian Frias wrote: > >> > >> What concrete solution do you propose? > > > > I have already proposed two solutions. > > > > A) Request a channel only when you need it. Obviously we can't do virtual > > channels with this (though we should still use virt-channels framework). > > The sbox setup and teardown can be done as part of channel request and > > freeup. PL08x already does this. > > > > Downside is that we can only have as many consumers at a time as channels. > > > > I have not heard any technical reason for not doing this apart from drivers > > grab the channel at probe, which is incorrect and needs to be fixed > > irrespective of the problem at hand. > > > > This is my preferred option. > > There is one important drawback with this solution. If a driver calls > dma_request_chan() when no channels are currently available, it will > get -EBUSY. If there were a flag in dma_request_chan to be put to > sleep (with timeout) until a channel is available, then it would > work. But busy waiting in the client driver is a waste of power. Right, but in that case the fallback would be PIO mode, and if that is not availble (IIRC some f your devices don't) then reject the usage with EAGAIN. -- ~Vinod -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
