Hi Peter, On Thursday 03 Nov 2016 11:23:50 Peter Ujfalusi wrote: > On 11/02/2016 11:19 PM, Laurent Pinchart wrote: > > On Wednesday 02 Nov 2016 14:39:59 Peter Ujfalusi wrote: > >> With the new dma_request_chan() the client driver does not need to look > >> for the DMA resource and it does not need to pass filter_fn anymore. > >> By switching to the new API the driver can now support deferred probing > >> against DMA. > > > > I believe this breaks the OMAP3 ISP driver. > > dma_request_slave_channel_compat() is a superset of dma_request_chan() > > that will, when called with omap_dma_filter_fn, return as a fallback any > > free channel handled by the OMAP DMA engine driver. This feature is > > actively used by this driver and must be preserved. > > The fallback to use the filter_fn is used only when booted in legacy > mode or when requesting a channel for non slave DMA operation. > Based on the code in the driver it is handling slave transfers, so it > must have DMA request line coming from somewhere. If that is missing the > driver should not be able to work as it will not start the transfer. If I remember correctly, the OMAP3 ISP has no dedicated DMA channel is it doesn't issue any hardware trigger. It can use any DMA channel, and performs a memcpy-like operation from a FIFO exposed through a single register to a system memory location. > dma_request_chan() is to be used when you want to have slave channel > with DMA request. > > If legacy mode needs to be supported then adding the hist DMA request > number to the omap3xxx_sdma_map in arch/arm/mach-omap2/dma.c should be done. > The reason the omap3isp is not in the table is that I could not find any > place where the DMA resource was set (nor the DMA is specified in DT). That's because there's no DMA request number for the OMAP3 ISP :-) > I'm unsure how this driver could work w/o DMA request line over a random > (and SW triggered) DMA channel with slave operation. For the slave DMA > you need to have DMA request line. As far as I understand, the DMA channel is software triggered, and the DMA engine will just perform the programmed number of transfers, without waiting for a hardware trigger. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
