platform/x86: asus-wmi: fix screenpad power state detection

On some models, e.g. the UX5400EA, the screenpad power state cannot be
read back: DSTS(ASUS_WMI_DEVID_SCREENPAD_POWER) never sets
ASUS_WMI_DSTS_STATUS_BIT, so asus_wmi_get_devstate_simple() reports the
panel as powered off regardless of its real state.

The DSDT shows DSTS 0x00050031 (POWER) and DSTS 0x00050032 (LIGHT)
both read the same two-byte EC register, each returning a different
byte: byte 0 is a raw EC status byte, which is 0xa0 when the panel is
powered and 0x00 when it is off, and byte 1 is the brightness. Read
the power state from the low byte instead of
ASUS_WMI_DSTS_STATUS_BIT: firmware reporting the power through the
status bit is covered too, since ASUS_WMI_DSTS_STATUS_BIT lies inside
ASUS_WMI_DSTS_BRIGHTNESS_MASK.

Reuse read_screenpad_backlight_power() in asus_screenpad_init() in
place of the raw devstate read. This makes the brightness read
reachable on models like the UX5400EA, so mask the SCREENPAD_LIGHT
value with ASUS_WMI_DSTS_BRIGHTNESS_MASK before storing it: the
unmasked devstate (0x0001ffa0 when the panel is on) would otherwise be
exposed to userspace as an out-of-range brightness (max_brightness is
255) which systemd-backlight then persists.

While at it, pass asus_wmi_get_devstate() the u32 it expects.

Fixes: 130d29c5627c ("platform/x86: asus-wmi: adjust screenpad power/brightness handling")
Reported-by: Hugo Baigue <hugobaigue2004@gmail.com>
Closes: https://lore.kernel.org/all/CAO84+x+P2_xyHP89+nGVSMV6bL+dy0P9=vyEEfZGnFhv0hBNWw@mail.gmail.com/
Suggested-by: Hugo Baigue <hugobaigue2004@gmail.com>
Tested-by: Hugo Baigue <hugobaigue2004@gmail.com>
Cc: stable@vger.kernel.org
Assisted-by: zcode:glm-5.3-flash
Signed-off-by: Denis Benato <denis.benato@linux.dev>
Link: https://patch.msgid.link/20260916143838.170950-3-denis.benato@linux.dev
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

0 files changed, 0 insertions, 0 deletions