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This workaround is specific for a particular panel on Google
chromebook project. When user space daemon enter idle state.
It request adjust brightness to 0, turn backlight_enable signal
off and keep eDP main link active.
On general LCD, this behavior might not be a problem.
But on this panel, its tcon would expect source to execute
full eDP power off sequence after drop backlight_enable signal.
Without eDP power off sequence. Even source try to turn
backlight_enable signal on and restore proper brightness level.
This panel is not able to light on again.
This WA ignored the request from user space daemon to disable
backlight_enable signal and keep it on always. When user space
request kernel to turn eDP display off, kernel driver still
can control backlight_enable signal properly. It would not
impact standard eDP power off sequence.
v2: 1. modify the quirk name and debug messages.
2. unregister backlight.power callback for specific device.
v3: 1. modify debug output messages.
2. use DMI_EXACT_MATCH instead of DMI_MATCH.
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Cooper Chiou <cooper.chiou@intel.com>
Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210624053932.21037-1-shawn.c.lee@intel.com
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>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200221172927.510027-2-hdegoede@redhat.com