[Letux-kernel] backlight woes

Andreas Kemnade andreas at kemnade.info
Thu Mar 21 22:15:59 CET 2019


Hi,

I finally debugged a bit more the backlight thing.
What fails:

drivers/video/backlight/pwm_bl.c
static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb)
...
/* The PWM is disabled, keep it like this */
   if (!pwm_is_enabled(pb->pwm))
        return FB_BLANK_POWERDOWN;


That sets power state to 4 initially.
If we have
drm/omap: panel-tpo-td028ttec1: add backlight support
in, it will be enabled later on.

So the interesting thing is whether the whole thing can be considered
a regression and that panel patch the solution...
So we could have some arguments to bring it into 5.1.
Next question: why does this pwm_is_enabled fail.
Maybe the problem was already there is 5.0...

So the display problem is really another one.
I am using this as an init script for those tests now
(init=/disp-test.sh)

root at gta04:~# cat /disp-test.sh 
#!/bin/bash
OLDCUR=0
PATH=/usr/local/bin:$PATH
mount -t sysfs none /sys
mount -t debugfs none /sys/kernel/debug
mount -t proc none /proc
mount -t tmpfs none /measure
echo 1 > /sys/kernel/debug/pm_debug/enable_off_mode

modprobe omapdrm
modprobe connector_analog_tv
modprobe encoder_opa362 
modprobe panel_tpo_td028ttec1
modprobe panel_dpi
modprobe omapdss

modprobe pwm_omap_dmtimer
sleep 2
modprobe pwm_bl
sleep 3

uname -r | qrencode -s 10 -o /measure/q.png
fbpng /measure/q.png
sleep 5

exec /sbin/init "$@"
root at gta04:~# 

Regards,
Andreas



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