Re: PROBLEM: [Toshiba Portege Z835] Brightness control lost after suspend

Re: PROBLEM: [Toshiba Portege Z835] Brightness control lost after suspend

[Aaron Lu]

On Thu, Jul 31, 2014 at 10:05:14PM +0100, John Marsden wrote:
> On 31 July 2014 09:09, Aaron Lu <aaron.lu@intel.com> wrote:
> > Please add acpi_backlight=vendor to kernel cmdline and see if that makes
> > the backlight work. What it does is to tell ACPI video module not to
> > create the acpi_videoX sysfs interface and let's see if X server will
> > pick up the intel_backlight one.
> 
> Adding acpi_backlight=vendor to the kernel cmdline results in the
> brightness controls not working from first boot, not just after a
> suspend.

That probably because X server now picks the toshiba_acpi interface
instead of the intel_backlight one.

A workaround from user space is to specify the backlight interface you
want to use in xorg.conf, an example is here:
https://bugs.debian.org/cgi-bin/bugreport.cgi?msg=78;att=0;bug=651741

Section "Device"
Identifier  "Intel Graphics"
Driver      "intel"
Option      "AccelMethod"     "sna"
Option      "Backlight" "intel_backlight"
Driver      "intel"
BusID       "PCI:0:2:0"
EndSection

Alternatively, we can disable the acpi_video and toshiba_acpi interfaces
in the kernel so that only intel_backlight is available. I'm not sure
how to do this nicely, I've cc-ed platform x86 mailing list.

Regards,
Aaron

> 
> Detailed test results:
> 
> After fresh boot into 3.16-rc with acpi_backlight=vendor added to the
> kernel cmdline
> ls -l /sys/class/backlight
> total 0
> lrwxrwxrwx 1 root root 0 Jul 31 21:38 intel_backlight ->
> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight
> lrwxrwxrwx 1 root root 0 Jul 31 21:38 toshiba ->
> ../../devices/LNXSYSTM:00/LNXSYBUS:00/TOS6208:00/backlight/toshiba
> 
> Attempts to adjust brightness via user interfaces (system settings and
> function keys) fail to change brightness.
> 
> It remains possible to adjust brightness by directly writing to
> /sys/class/backlight/intel_backlight/brightness but, as before, not by
> writing to  /sys/class/backlight/toshiba/brightness.
> 
> After suspend and resume same test results.
> 
> Regards,  John

Re: PROBLEM: [Toshiba Portege Z835] Brightness control lost after suspend

[John Marsden]

On 1 August 2014 03:42, Aaron Lu <aaron.lu@intel.com> wrote:
> A workaround from user space is to specify the backlight interface you
> want to use in xorg.conf, an example is here:
> https://bugs.debian.org/cgi-bin/bugreport.cgi?msg=78;att=0;bug=651741
>
> Section "Device"
> Identifier  "Intel Graphics"
> Driver      "intel"
> Option      "AccelMethod"     "sna"
> Option      "Backlight" "intel_backlight"
> Driver      "intel"
> BusID       "PCI:0:2:0"
> EndSection

Thank you.  This works both in v3.16-rc and in the current Ubuntu
14.04 latest update.  Now user-interface brightness controls work
before AND after a suspend.  The only difference in the user
experience is that now minimum brightness on the brightness sliders
gives a completely dark screen rather than just a very dimly lit
screen.  I can live with this.

I'm guessing this should be regarded as a work-round rather than a
final solution that might eventually form part of the kernel.  Should
I report it as such back in the downstream Ubuntu/Launchpad bug?

If in future, when this is addressed in the kernel, further testing is
required please let me know.  I'd be happy to assist.

Thank you for your help,

John Marsden