On Mon, May 11, 2020 at 12:58:13PM +0100, Mark Brown wrote: > On Mon, May 11, 2020 at 05:10:16AM +0300, Serge Semin wrote: > > > Alas linearizing the SPI messages won't help in this case because the DW DMA > > driver will split it into the max transaction chunks anyway. > > That sounds like you need to also impose a limit on the maximum message > size as well then, with that you should be able to handle messages up > to whatever that limit is. There's code for that bit already, so long > as the limit is not too low it should be fine for most devices and > client drivers can see the limit so they can be updated to work with it > if needed. Hmm, this might work. The problem will be with imposing such limitation through the DW APB SSI driver. In order to do this I need to know: 1) Whether multi-block LLP is supported by the DW DMA controller. 2) Maximum DW DMA transfer block size. Then I'll be able to use this information in the can_dma() callback to enable the DMA xfers only for the safe transfers. Did you mean something like this when you said "There's code for that bit already" ? If you meant the max_dma_len parameter, then setting it won't work, because it just limits the SG items size not the total length of a single transfer. So the question is of how to export the multi-block LLP flag from DW DMAc driver. Andy? -Sergey
