Re: [PATCH v2 2/4] dma: xilinx: dpdma: Add the Xilinx DisplayPort DMA engine driver

Vinod Koul
2019-12-20T08:01:34Z

Hi Laurent,

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

> 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?

--
~Vinod