Here's a series from Boris for enabling SDTV output on VC4. There are two other patches to the clk subsystem necessary to get it working, which I'm in the process of reviewing.
I've tested it on composite input of a monitor I had laying around, and it's basically working. Booting with the firmware bringing up SDTV, I get an image "fine" (to the extent that SDTV is ever fine). If I boot with firmware bringing up HDMI and switch to VEC later, then the image is gray, but the clock got set to 106Mhz instead of 108 so this is probably not a DRM bug.
This series was entirely written by Boris, but I've got the permission to send it out so it's being routed through me.
Boris Brezillon (6): drm/vc4: Fix ->clock_select setting for the VEC encoder drm: Add TV connector states to drm_connector_state drm/vc4: Add support for the VEC (Video Encoder) IP drm/vc4: Document VEC DT binding ARM: bcm/dt: Add VEC node in bcm283x.dtsi ARM: bcm/dt: Enable the VEC IP on all RaspberryPi boards
.../devicetree/bindings/display/brcm,bcm-vc4.txt | 14 + arch/arm/boot/dts/bcm2835-rpi.dtsi | 5 + arch/arm/boot/dts/bcm283x.dtsi | 8 + drivers/gpu/drm/drm_atomic.c | 50 ++ drivers/gpu/drm/vc4/Makefile | 1 + drivers/gpu/drm/vc4/vc4_crtc.c | 38 +- drivers/gpu/drm/vc4/vc4_debugfs.c | 1 + drivers/gpu/drm/vc4/vc4_drv.c | 1 + drivers/gpu/drm/vc4/vc4_drv.h | 6 + drivers/gpu/drm/vc4/vc4_regs.h | 3 +- drivers/gpu/drm/vc4/vc4_vec.c | 657 +++++++++++++++++++++ include/drm/drm_connector.h | 32 + 12 files changed, 800 insertions(+), 16 deletions(-) create mode 100644 drivers/gpu/drm/vc4/vc4_vec.c