The VPU embeds a "Register DMA" that can write a sequence of registers on the VPU AHB bus, either manually or triggered by an internal IRQ event like VSYNC or a line input counter.
The initial implementation handles a single channel (over 8), triggered by the VSYNC irq and does not handle the RDMA irq.
The RDMA will be usefull to reset and program the AFBC decoder unit on each vsync without involving the interrupt handler that can be masked for a long period of time, producing display glitches.
For this we use the meson_rdma_writel_sync() which adds the register write tuple (VPU register offset and register value) to the RDMA buffer and write the value to the HW.
When enabled, the RDMA is enabled to rewritte the same sequence at the next VSYNC event, until a new buffer is committed to the OSD plane.
The the Amlogic G12A is switched to RDMA, the Amlogic GXM Decoder doesn't need a reset/reprogram at each vsync.
Neil Armstrong (3): drm/meson: add RDMA register bits defines drm/meson: add RDMA module driver drm/meson: use RDMA to reconfigure AFBC on vsync
drivers/gpu/drm/meson/Makefile | 2 +- drivers/gpu/drm/meson/meson_crtc.c | 27 ++---- drivers/gpu/drm/meson/meson_drv.c | 14 ++- drivers/gpu/drm/meson/meson_drv.h | 6 ++ drivers/gpu/drm/meson/meson_osd_afbcd.c | 100 ++++++++++--------- drivers/gpu/drm/meson/meson_rdma.c | 123 ++++++++++++++++++++++++ drivers/gpu/drm/meson/meson_rdma.h | 20 ++++ drivers/gpu/drm/meson/meson_registers.h | 48 +++++++++ 8 files changed, 273 insertions(+), 67 deletions(-) create mode 100644 drivers/gpu/drm/meson/meson_rdma.c create mode 100644 drivers/gpu/drm/meson/meson_rdma.h