Hi Laurent, On 2019-11-01 09:43, Laurent Pinchart wrote: > Hello, > > I'm looking at the available options to support overlays in the display > pipeline of the i.MX7. The LCDIF itself unfortunaltey doesn't support > overlays, the feature being implemented in the PXP. A driver for the PXP > is available but only supports older SoCs whose PXP doesn't support > overlays. This driver is implemented as a V4L2 mem2mem driver, which > makes support of additional input channels impossible. Thanks for bringing this up, it is a topic I have wondered too: Interaction between PXP and mxsfb. I am not very familiar with the V4L2 subsystem so take my opinions with a grain of salt. > > Here are the options I can envision: > > - Extend the existing PXP driver to support multiple channels. This is > technically feasible, but will require moving away from the V4L2 > mem2mem framework, which would break userspace. I don't think this > path could lead anywhere. > > - Write a new PXP driver for the i.MX7, still using V4L2, but with > multiple video nodes. This would allow blending multiple layers, but > would require writing the output to memory, while the PXP has support > for direct connections to the LCDIF (through small SRAM buffers). > Performances would thus be suboptimal. The API would also be awkward, > as using the PXP for display would require usage of V4L2 in > applications. So the video nodes would be sinks? I would expect overlays to be usable through KMS, I guess that would then not work, correct? > > - Extend the mxsfb driver with PXP support, and expose the PXP inputs as > KMS planes. The PXP would only be used when available, and would be > transparent to applications. This would however prevent using it > separately from the display (to perform multi-pass alpha blending for > instance). KMS planes are well defined and are well integrated with the KMS API, so I prefer this option. But is this compatible with the currently supported video use-case? E.g. could we make PXP available through V4L2 and through DRM/mxsfb? Not sure what your use case is exactly, but when playing a video I wonder where is the higher value using PXP: Color conversion and scaling or compositing...? I would expect higher value in the former use case. > > What would be the best option going forward ? Would any of you, by any > chance, have already started work in this area ? I have not worked in that area, so feel free! -- Stefan
