The Thundersoft TST178 tablet uses a DSI panel with an external PWM controller (as all DSI panels do). But unlike other DSI panels a duty-cycle of 100% turns the backlight off and 0% sets it to maximum brightness.
I've checked the VBT and there is a BDB_LVDS_BACKLIGHT section, but it does not set the active_low_pwm flag. This tablet re-uses the main PCI vendor and product ids for the subsystem ids, so I see no other option then to add a DMI based quirk to fix this.
Note that the PWM backlight code in intel_panel.c currently does not honor the vbt.active_low_pwm flag, but that does not matter in this case.
Signed-off-by: Hans de Goede hdegoede@redhat.com --- drivers/gpu/drm/i915/display/intel_quirks.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/drivers/gpu/drm/i915/display/intel_quirks.c b/drivers/gpu/drm/i915/display/intel_quirks.c index 399b1542509f..54dba152ead8 100644 --- a/drivers/gpu/drm/i915/display/intel_quirks.c +++ b/drivers/gpu/drm/i915/display/intel_quirks.c @@ -82,6 +82,16 @@ static const struct intel_dmi_quirk intel_dmi_quirks[] = { DMI_MATCH(DMI_PRODUCT_NAME, ""), }, }, + { + .callback = intel_dmi_reverse_brightness, + .ident = "Thundersoft TST178 tablet", + /* DMI strings are too generic, also match on BIOS date */ + .matches = {DMI_EXACT_MATCH(DMI_BOARD_VENDOR, "AMI Corporation"), + DMI_EXACT_MATCH(DMI_BOARD_NAME, "Aptio CRB"), + DMI_EXACT_MATCH(DMI_PRODUCT_NAME, "To be filled by O.E.M."), + DMI_EXACT_MATCH(DMI_BIOS_DATE, "04/15/2014"), + }, + }, { } /* terminating entry */ }, .hook = quirk_invert_brightness,