Hi Laurent, On Fri, 2019-11-01 at 10:43 +0200, 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. > > 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. I may be biased, but please don't break the V4L2 mem2mem usecase :) > - 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. I'm not sure V4L2 is the best API for multi-pass 2D composition, especially as the PXP is able to blit an overlay onto a background in place. > - 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). For the SRAM block row buffer path to the LCDIF, I think the KMS plane abstraction is the way to go. The DRM and V4L2 drivers could be made to use a shared backend, such that only one of plane composition and V4L2 scaling/CSC functions can work at the same time. > 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 on this. regards Philipp
