c94cd0620a
Whenever the maximum BPC is changed, vc4_hdmi_encoder_compute_config()
might pick up a different BPC or format depending on the display
capabilities.
That change will have a number of side effects, including the clock
rates and whether the scrambling is enabled.
However, only drm_crtc_state.connectors_changed will be set to true,
since that properly only affects the connector.
This means that while drm_atomic_crtc_needs_modeset() will return true,
and thus drm_atomic_helper_commit_modeset_enables() will call our
encoder atomic_enable() hook, mode_changed will be false.
So crtc_set_mode() will not call our encoder .atomic_mode_set() hook. We
use this hook in vc4 to set the vc4_hdmi_connector_state.output_bpc (and
output_format), and will then reuse the value in .atomic_enable() to select
whether or not scrambling should be enabled.
However, since our clock rate is pre-computed during .atomic_check(), we
end up with the clocks properly configured, but the scrambling disabled,
leading to a blank screen.
Let's set mode_changed to true in our HDMI driver to force the update of
output_bpc, and thus prevent the issue entirely.
Fixes: ba8c0faebbb0 ("drm/vc4: hdmi: Enable 10/12 bpc output")
Signed-off-by: Dom Cobley <popcornmix@gmail.com>
Link: https://lore.kernel.org/r/20220613144800.326124-32-maxime@cerno.tech
Signed-off-by: Maxime Ripard <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.