Hi Laurent, On 20-12-19, 14:35, Laurent Pinchart wrote: > On Fri, Dec 20, 2019 at 01:31:27PM +0530, Vinod Koul wrote: > > On 20-12-19, 07:13, Laurent Pinchart wrote: > > > > > > OK, in the light of this information I'll keep the two separate and will > > > > switch to vchan as requested by Vinod. > > > > > > I've moved forward with this task, but eventually ran into one hack in > > > the driver that is more difficult to get rid of than the other ones. > > > > > > For display operation, the DPSUB driver needs to submit cyclic > > > interleaved transfer requests. There's no such thing (as far as I can > > > tell) in the DMA engine API, so the DPDMA drive simply keeps processing > > > > we do support interleave, you need to implement > > .device_prep_interleaved_dma and use dmaengine_prep_interleaved_dma() > > from the client > > I mean both interleaved and cyclic at the same time. > > > > the same descriptor over and over again until a new one is issued. The > > > hardware supports this with the help of hardware-based chaining of > > > descriptors, and the DPDMA driver simply sets the next pointer of the > > > descriptor to itself. > > > > > > How can I solve this in a way that wouldn't abuse the DMA engine API ? > > > > Is this not a cyclic case of descriptor? > > Exactly my point :-) It's cyclic, but has to be interleaved too as it's > a 2D transfer. IIRC the interleaved descriptor can be set in such a way that last chunk points to the first one.. I think Jassi had good ideas for generic interleave API which can do all this :) -- ~Vinod
