<html> <head> <base href="https://bugs.freedesktop.org/"> </head> <body> <div> <a class="bz_bug_link bz_status_NEEDINFO " title="NEEDINFO - Brightness control inversion from VBT table is not taken into account in Ubuntu 18.10" href="https://bugs.freedesktop.org/show_bug.cgi?id=111475#c5">Comment # 5</a> on <a class="bz_bug_link bz_status_NEEDINFO " title="NEEDINFO - Brightness control inversion from VBT table is not taken into account in Ubuntu 18.10" href="https://bugs.freedesktop.org/show_bug.cgi?id=111475">bug 111475</a> from <a class="email" href="mailto:szymon.balcerak@ts.fujitsu.com" title="Szymon <szymon.balcerak@ts.fujitsu.com>"> Szymon</a> <pre>Today I performed another tests a here are the results: 1. Confirmed that Linux does not take VBT backlight active low bit into consideration. If this is the bug that is to be decided by Linux graphic driver developers. NOTE: Windows graphic driver takes this setting into consideration. 2. Once BIOS writes 0xC8250 MMIO register with bit 29, backlight logic is inverted correctly. However 10% minimum brightness level defined in VBT table is NOT taken into account in this case, i.e. Linux brightness slider set at maximum produces complete darkness instead of 10% brightness (as set as minimum). 3. In comparison to point 2: Once backlight logic is inverted by kernel boot parameter acpi_backlight=vendor i915.invert_brightness=1, slider at max still respects minimum brightness level 10% defined in VBT.</pre> </div> <hr> You are receiving this mail because: <ul> <li>You are on the CC list for the bug.</li> <li>You are the QA Contact for the bug.</li> <li>You are the assignee for the bug.</li> </ul> </body> </html>