7fa846b95c
Issue is some displays go blank at the point of firmware to kms handover. Plugging/unplugging hdmi cable, power cycling display, or switching standby off/on typically resolve this case. Finally managed to find a display that suffers from this, and track down the issue. The firmware uses AVMUTE in normal operation. It will set AVMUTE before disabling hdmi clocks and phy. It will clear AVMUTE after clocks and phy are set up for a new hdmi mode. But with the hdmi handover from firmware to kms, AVMUTE will be set by firmware. kms driver typically has no GCP packet (except for deep colour modes). The spec isn't clear on whether to consider the AVMUTE as continuing indefinitely in the absence of a GCP packet, or to consider that state to have ended. Most displays behave as we want, but there are a number (from multiple manufacturers) which need to see AVMUTE cleared before displaying a picture. Lets just always enable GCP packet with AVMUTE cleared. That resolves the issue on problematic displays. From HDMI 1.4 spec: A CD field of zero (Color Depth not indicated) shall be used whenever the Sink does not indicate support for Deep Color. This value may also be used in Deep Color mode to transmit a GCP indicating only non-Deep Color information (e.g. AVMUTE). So use CD=0 where we were previously not enabling a GCP. Link: https://forum.libreelec.tv/thread/24780-le-10-0-1-rpi4-no-picture-after-update-from-le-10-0-0 Signed-off-by: Dom Cobley <popcornmix@gmail.com> Signed-off-by: Maxime Ripard <maxime@cerno.tech> Link: https://patchwork.freedesktop.org/patch/msgid/20230127161219.457058-1-maxime@cerno.tech
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.