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The pch_get_backlight(), lpt_get_backlight(), and lpt_set_backlight() functions operate directly on the hardware registers. If inverting the value is needed, using intel_panel_compute_brightness(), it should only be done in the interface between hardware registers and panel->backlight.level. The CPU mode takeover code added in commit5b1ec9ac7a("drm/i915/backlight: Fix backlight takeover on LPT, v3.") reads the hardware register and converts to panel->backlight.level correctly, however the value written back should remain in the hardware register "domain". This hasn't been an issue, because GM45 machines are the only known users of i915.invert_brightness and the brightness invert quirk, and without one of them no conversion is made. It's likely nobody's ever hit the problem. Fixes:5b1ec9ac7a("drm/i915/backlight: Fix backlight takeover on LPT, v3.") Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Lyude Paul <lyude@redhat.com> Cc: <stable@vger.kernel.org> # v5.1+ Reviewed-by: Lyude Paul <lyude@redhat.com> Signed-off-by: Jani Nikula <jani.nikula@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20210108152841.6944-1-jani.nikula@intel.com (cherry picked from commit0d4ced1c5b) Signed-off-by: Jani Nikula <jani.nikula@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.