On 12/01/2015 10:17 PM, Arnd Bergmann wrote: > On Tuesday 01 December 2015 22:29:54 Vinod Koul wrote: >> On Mon, Nov 30, 2015 at 03:45:30PM +0200, Peter Ujfalusi wrote: >>> channel via DT, ACPI or in case if the kernel booted in non DT/ACPI mode >>> it will use a filter lookup table and retrieves the needed information from >>> the dma_filter_map provided by the DMA drivers. >> >> That sounds right, for the third case would the arch, driver or someone else >> configure this? > > The typical case is for the configuration to be defined in arch or platform > code and passed down to the dmaengine driver. > > I just noticed that the text above (and probably the code too) should > be changed so we always fall back to this. There are cases where the > platform is booted with DT in principle, but the DMA engine does not > (yet) use DT and still wants to be converted. I think we can easily > handle that case by always trying this if the other methods fail. Yes, it was intentional actually to not fall back to legacy lookup. With the dma_request_slave_channel_compat() I have had cases when the DT binding was not correct - or actually when trying to get deferred working that the code would fall back to legacy mode and it got me a channel which is not usable. I did not know that we have platforms booting in DT but the dma binding is not working so it uses other method to get channel. I think, if we allow the fall back within dma_request_chan() it would not cause the same issue as the dma_request_slave_channel_compat() did as long as we are not providing the lookup table on DT booted cases when the DMA binding is working correctly. Let me see the flow, but I think it is doable. -- Péter -- 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
