On Thu, Apr 19, 2018 at 02:40:26PM +0300, Peter Ujfalusi wrote: > > On 2018-04-18 16:06, Lars-Peter Clausen wrote: > >> Hrm, true, but it is hardly the metadata use case. It is more like > >> different DMA transfer type. > > > > When I look at this with my astronaut architect view from high high up above > > I do not see a difference between metadata and multi-planar data. > > I tend to disagree. and we will love to hear more :) > > Both split the data that is sent to the peripheral into multiple > > sub-streams, each carrying part of the data. I'm sure there are peripherals > > that interleave data and metadata on the same data stream. Similar to how we > > have left and right channel interleaved in a audio stream. > > Slimbus, S/PDIF? > > > What about metadata that is not contiguous and split into multiple segments. > > How do you handle passing a sgl to the metadata interface? And then it > > suddenly looks quite similar to the normal DMA descriptor interface. > > Well, the metadata is for the descriptor. The descriptor describe the > data transfer _and_ can convey additional information. Nothing is > interleaved, the data and the descriptor are different things. It is > more like TCP headers detached from the data (but pointing to it). > > > But maybe that's just one abstraction level to high. > > I understand your point, but at the end the metadata needs to end up in > the descriptor which is describing the data that is going to be moved. > > The descriptor is not sent as a separate DMA trasnfer, it is part of the > DMA transfer, it is handled internally by the DMA. That is bit confusing to me. I thought DMA was transparent to meta data and would blindly collect and transfer along with the descriptor. So at high level we are talking about two transfers (probably co-joined at hip and you want to call one transfer) but why can't we visualize this as just a DMA transfers. maybe you want to signal/attach to transfer, cant we do that with additional flag DMA_METADATA etc..? -- ~Vinod -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
