On Tue, May 31, 2016 at 04:19:28PM +0200, Michal Suchanek wrote: > On 31 May 2016 at 15:27, Mark Brown <broonie@xxxxxxxxxx> wrote: > > On Tue, May 31, 2016 at 12:44:54PM +0200, Michal Suchanek wrote: > >> On 30 May 2016 at 17:50, Mark Brown <broonie@xxxxxxxxxx> wrote: > >> > On Mon, May 30, 2016 at 05:28:10PM +0200, Michal Suchanek wrote: > > > >> >> It's what the driver did to start with and it was requested to fall > >> >> back to non-DMA in the case DMA is not available. > > > >> > Why? I really can't see any sensible use case for this that doesn't > >> > have a better solution available. > > > >> Of course, the solution is to compile in the DMA driver. > > > >> It's been argued that some drivers which use only short transfers will > >> just work. > > > > With nothing else in the system that needs DMA? It's making the > > performance of the system less reliable for the benefit of a very narrow > > use case. > > Some of the platform devices have dedicated DMA *controller* built > into the device IP so the DMA engine really is optional on many sunxi > devices. Besides SPI you definitely need the DMA engine for audio. You > probably don't need it for storage and graphics. I don't have any idea > if it's used for USB and Ethernet. USB and Ethernet have their own dedicated DMA engines. So currently, the only driver that requires it is the audio codec. Maxime -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com
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