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In commit7994672309("drm/i915: Assume 100% brightness when not in DPCD control mode"), we fixed the brightness level when DPCD control was not active to max brightness. This is as good as we can guess since most backlights go on full when uncontrolled. However in doing so we changed the semantics of the initial 'backlight.enabled' value. At least on Pixelbooks, they were relying on the brightness level in DP_EDP_BACKLIGHT_BRIGHTNESS_MSB to be 0 on boot such that enabled would be false. This causes the device to be enabled when the brightness is set. Without this, brightness control doesn't work. So by changing brightness to max, we also flipped enabled to be true on boot. To fix this, make enabled a function of brightness and backlight control mechanism. Fixes:7994672309("drm/i915: Assume 100% brightness when not in DPCD control mode") Cc: Lyude Paul <lyude@redhat.com> Cc: Jani Nikula <jani.nikula@intel.com> Cc: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com> Cc: "Ville Syrjälä" <ville.syrjala@linux.intel.com> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com> Cc: Kevin Chowski <chowski@chromium.org>> Signed-off-by: Sean Paul <seanpaul@chromium.org> Reviewed-by: Lyude Paul <lyude@redhat.com> Signed-off-by: Lyude Paul <lyude@redhat.com> Link: https://patchwork.freedesktop.org/patch/msgid/20200918002845.32766-1-sean@poorly.run (cherry picked from commit4ade8f31c2) Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
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.