It turns out that additional logic between HDMI CEC controller and pins on PHY on some Allwinner SoCs prevents proper communication. It might be possible to fix it, but it's much easier and less error prone to just directly drive pins using software implementation of CEC protocol.
Let me know what do you think.
Best regards, Jernej
Jernej Skrabec (2): drm/bridge/synopsys: dw-hdmi: Add an option to suppress loading CEC driver drm/sun4i: dw-hdmi: Bit bang CEC on some SoCs
drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 2 +- drivers/gpu/drm/sun4i/Kconfig | 10 +++ drivers/gpu/drm/sun4i/sun8i_dw_hdmi.h | 11 +++ drivers/gpu/drm/sun4i/sun8i_hdmi_phy.c | 83 ++++++++++++++++++++++- include/drm/bridge/dw_hdmi.h | 2 + 5 files changed, 105 insertions(+), 3 deletions(-)