Hi, If the i915 driver is being used then the sysfs option should be /sys/class/backlight/intel_backlight/brightness. If the intel_backlight path is not present, then the best thing is to enable debug by adding drm.debug =0xe to the kernel command line as Vincent suggested to see what is going on.
Regards, Yetunde From: Cheah, Vincent Beng Keat Sent: Thursday, November 26, 2015 6:29 AM To: Chang, Rebecca Swee Fun; Prasant J; Ahmad, Mohd Azril; Adebisi, YetundeX Cc: [email protected] Subject: RE: [meta-intel] Intel Atom E3845: Backlight control +Yetunde. Hi PJ, I don’t think we have tried the xrandr option to do backlight but I believe you should be able to control LVDS backlight simply by accessing this sysfs --> /sys/class/backlight/acpi_video0/brightness (hmm… this looks pretty much like what you have done below – referring to the PCI path). Could you please add drm.debug =0xe to enable DRM debug to see what is going on down there. Also, it would definitely be nice if you can make your image in run-level-3 to isolate the user-space from the kernel side when you are testing this. URL: https://wiki.archlinux.org/index.php/Backlight … Vincent From: Chang, Rebecca Swee Fun Sent: Thursday, November 26, 2015 8:41 AM To: Prasant J <[email protected]<mailto:[email protected]>>; Cheah, Vincent Beng Keat <[email protected]<mailto:[email protected]>>; Ahmad, Mohd Azril <[email protected]<mailto:[email protected]>> Cc: [email protected]<mailto:[email protected]> Subject: RE: [meta-intel] Intel Atom E3845: Backlight control Hi Vincent/ Azril, Can you help to provide advice to Pj? Thanks. Regards, Rebecca From: [email protected]<mailto:[email protected]> [mailto:[email protected]] On Behalf Of Prasant J Sent: Wednesday, November 25, 2015 8:46 PM To: [email protected]<mailto:[email protected]> Subject: [meta-intel] Intel Atom E3845: Backlight control Hi, I'm using Intel Atom E3845 with my custom hardware. I have an LVDS display and I would like to control the brightness from the linux shell. I used the command: xrandr --output DP2 --brightness <val> This command (I think) changes the gamma factor of the display but the actual back light intensity is not changed. I tried changing the value of: /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness but still no change in the back light intensity. Any inputs on how can I control the back light intensity of my LVDS display? Regards, Pj
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