LogicBricks is a vendor of numerous IP blocks, ranging from display controllers, audio controllers, 3D accelerators and many other specialized IP blocks. Most of these IP blocks are designed to work with the Xilinx Zynq 7000 system-on-chip, which includes an FPGA area. And indeed, because the Zynq 7000 does not have a display controller, one of Bootlin customers has selected the LogicBricks logiCVC-ML IP to provide display support for their Zynq 7000 design.
LogiBricks provide one driver based on the framebuffer subsystem and another one based on the DRM subsystem, but none of these drivers are in the upstream Linux kernel. Bootlin engineer Paul Kocialkowski worked on a clean DRM driver for this IP block, and submitted the first version to the upstream Linux kernel. We already received some useful comments on the Device Tree binding for this IP block, which is pretty elaborate due to the number of aspects/features that can be tuned at IP synthesis time, and we will of course take into account those comments and send new iterations of the patch series until it gets merged.
In the e-mail containing the driver patch itself, Paul gives a summary of the IP features that are supported and tested, and those that re either untested or unsupported:
Introduces a driver for the LogiCVC display controller, a programmable logic controller optimized for use in Xilinx Zynq-7000 SoCs and other Xilinx FPGAs. The controller is mostly configured at logic synthesis time so only a subset of configuration is left for the driver to handle. The following features are implemented and tested: - LVDS 4-bit interface; - RGB565 pixel formats; - Multiple layers and hardware composition; - Layer-wide alpha mode; The following features are implemented but untested: - Other RGB pixel formats; - Layer framebuffer configuration for version 4; - Lowest-layer used as background color; - Per-pixel alpha mode. The following features are not implemented: - YUV pixel formats; - DVI, LVDS 3-bit, ITU656 and camera link interfaces; - External parallel input for layer; - Color-keying; - LUT-based alpha modes. Additional implementation-specific notes: - Panels are only enabled after the first page flip to avoid flashing a white screen. - Depth used in context of the LogiCVC driver only counts color components to match the definition of the synthesis parameters. Support is implemented for both version 3 and 4 of the controller. With version 3, framebuffers are stored in a dedicated contiguous memory area, with a base address hardcoded for each layer. This requires using a dedicated CMA pool registered at the base address and tweaking a few offset-related registers to try to use any buffer allocated from the pool. This is done on a best-effort basis to have the hardware cope with the DRM framebuffer allocation model and there is no guarantee that each buffer allocated by GEM CMA can be used for any layer. In particular, buffers allocated below the base address for a layer are guaranteed not to be configurable for that layer. See the implementation of logicvc_layer_buffer_find_setup for specifics. Version 4 allows configuring each buffer address directly, which guarantees that any buffer can be configured.