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Commit9d44abbbb8("drm/vc4: Fall back to using an EDID probe in the absence of a GPIO.") added some code to read the EDID through DDC in the HDMI driver detect hook since the Pi3 had no HPD GPIO back then. However, commitb1b8f45b31("ARM: dts: bcm2837: Add missing GPIOs of Expander") changed that a couple of years later. This causes an issue though since some TV (like the LG 55C8) when it comes out of standy will deassert the HPD line, but the EDID will remain readable. It causes an issues nn platforms without an HPD GPIO, like the Pi4, where the DDC probing will be our primary mean to detect a display, and thus we will never detect the HPD pulse. This was fine before since the pulse was small enough that we would never detect it, and we also didn't have anything (like the scrambler) that needed to be set up in the display. However, now that we have both, the display during the HPD pulse will clear its scrambler status, and since we won't detect the disconnect/reconnect cycle we will never enable the scrambler back. As our main reason for that DDC probing is gone, let's just remove it. Signed-off-by: Maxime Ripard <maxime@cerno.tech> Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com> Link: https://lore.kernel.org/r/20211025152903.1088803-2-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.