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25dd390c62
Panasonic laptops (at least from CF-W4 onwards) have dedicated firmware registers for saving ac/dc and current brightness. They are a bit confusing so here's some explanations: AC_MIN_BRIGHT, AC_MAX_BRIGHT, DC_MIN_BRIGHT, DC_MAX_BRIGHT: Read-only. Values: 0x01 and 0x15 respectively. AC_CUR_BRIGHT, DC_CUR_BRIGHT: Read-Write. 0x00-0xFF. Store user-defined AC/DC brightness. However, they do not represent current brightness so they should be named AC_BRIGHT and DC_BRIGHT instead. CUR_BRIGHT (present since CF-W4): Read-Write. 0x00-0xFF. It sets the current brightness. It won't update itself if brightness is changed via other means, e.g. acpi_video0. Another CUR_BRIGHT (added since CF-W5): Read-Write. 0x01-0x15. Its value always synchronizes with current brightness. Not implemented in this version. Currently the backlight API interacts with AC_CUR_BRIGHT (probably because it's the only bl register available in earlier models?). This patch adds sysfs attributes for AC_CUR_BRIGHT, DC_CUR_BRIGHT and CUR_BRIGHT. It also fixes the error of https://lkml.org/lkml/2020/8/19/1264. PS: I think the backlight API should interact with CUR_BRIGHT instead of AC_CUR_BRIGHT. But it involves complications like mapping between 0x01-0x15 or 0x00-0x14 (the backlight API) and 0x00-0xFF (CUR_BRIGHT). I'll leave the discussion for a later version. Signed-off-by: Kenneth Chan <kenneth.t.chan@gmail.com> Link: https://lore.kernel.org/r/20200821181433.17653-10-kenneth.t.chan@gmail.com Signed-off-by: Hans de Goede <hdegoede@redhat.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.