On Mon, May 11, 2020 at 06:48:00PM +0100, Mark Brown wrote: > On Mon, May 11, 2020 at 04:58:53PM +0300, Andy Shevchenko wrote: > > On Mon, May 11, 2020 at 4:48 PM Serge Semin > > > > So the question is of how to export the multi-block LLP flag from DW DMAc > > > driver. Andy? > > > I'm not sure I understand why do you need this being exported. Just > > always supply SG list out of single entry and define the length > > according to the maximum segment size (it's done IIRC in SPI core). > > If there's a limit from the dmaengine it'd be a bit cleaner to export > the limit from the DMA engine (and it'd help with code reuse for clients > that might work with other DMA controllers without needing to add custom > compatibles for those instantiations). Right. I've already posted a patch which exports the max segment size from the DW DMA controller driver. The SPI core will get the limit in the spi_map_buf() method by calling the dma_get_max_seg_size() function. The problem I described concerns of how to determine whether to apply the solution Andy suggested, since normally if DW DMA controller has true multi-block LLP supported the workaround isn't required. So in order to solve the problem in a generic way the easiest way would be to somehow get the noLLP flag from the DW DMAC private data and select a one-by-one SG entries submission algorithm instead of the normal one... On the other hand we could just implement a flag-based quirks in the DW APB SSI driver and determine whether the LLP problem exists for the platform-specific DW APB SSI controller. -Sergey
