[meta-intel] Intel Atom E3845: Backlight control

[Adebisi, YetundeX]

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: meta-intel at yoctoproject.org
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 <pj0585 at gmail.com<mailto:pj0585 at gmail.com>>; Cheah, Vincent Beng Keat <vincent.beng.keat.cheah at intel.com<mailto:vincent.beng.keat.cheah at intel.com>>; Ahmad, Mohd Azril <mohd.azril.ahmad at intel.com<mailto:mohd.azril.ahmad at intel.com>>
Cc: meta-intel at yoctoproject.org<mailto:meta-intel at yoctoproject.org>
Subject: RE: [meta-intel] Intel Atom E3845: Backlight control

Hi Vincent/ Azril,

Can you help to provide advice to Pj?
Thanks.

Regards,
Rebecca

From: meta-intel-bounces at yoctoproject.org<mailto:meta-intel-bounces at yoctoproject.org> [mailto:meta-intel-bounces at yoctoproject.org] On Behalf Of Prasant J
Sent: Wednesday, November 25, 2015 8:46 PM
To: meta-intel at yoctoproject.org<mailto:meta-intel at yoctoproject.org>
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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