Re: drm2 regression: backlight adjustment on ivybridge no longer works

On Sun, Feb 01, 2015 at 10:41:25AM +0100, Lars Engels wrote:
> On Sun, Feb 01, 2015 at 03:35:15AM -0600, Andrew Wilcox wrote:
> > Lars Engels sent: 01 February 2015 03:18:
> > > With acpi_video I get some interesting sysctl:
> > > hw.acpi.video.lcd0.levels: 100 100 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
> > > 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
> > > 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63
> > > 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87
> > > 88 89 90 91 92 93 94 95 96 97 98 99 100
> > > 
> > > I guess it should not be 100 100 0 ... 100?
> > 
> > Actually, the "standard" internal ACPI brightness level struct (BRTN in the DSDT) is laid out as:
> > 
> > * "Full power" value (one byte, the value at which the brightness should be set on AC by default)
> > * "Economy" value (one byte, the value at which the brightness should be set on battery by default)
> > * Actual values (N bytes, up to Max but frequently not)
> > 
> > So, no, that value indeed sounds correct.  On my laptop the value is:
> > 80 47 0 7 13 20 27 33 40 47 53 60 67 73 80 87 93 100
> 
> Thank you for the explanation.
> FWIW, here is the full output from sysctl hw.acpi.video.lcd0:
> 
> hw.acpi.video.lcd0.active: 1
> hw.acpi.video.lcd0.brightness: 11
> hw.acpi.video.lcd0.fullpower: 100
> hw.acpi.video.lcd0.economy: 100
> hw.acpi.video.lcd0.levels: 100 100 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
> 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
> 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63
> 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87
> 88 89 90 91 92 93 94 95 96 97 98 99 100
> hw.acpi.video.crt0.active: 1
> hw.acpi.video.ext0.active: 1
> hw.acpi.video.ext1.active: 1
> hw.acpi.video.ext2.active: 1
> hw.acpi.video.ext3.active: 1
> hw.acpi.video.ext4.active: 1
> hw.acpi.video.ext5.active: 1
> 
> > 
> > What revision of -CURRENT are you running?  What is the outcome of
> > trying the patch posted Saturday morning (UTC) from Elizabeth Myers
> > (message ID <54CC5311.9070604_at_interlinked.me>)?
> > 
> 
> I'm currently running r277858 and haven't tried the patch, yet. But will
> do now and report back.
> 

So now I have a new sysctl hw.dri.0.i915_backlight. But no matter what
value I pass to it, the brightness doesn't change.

It's a Ivy Brigde notebook where drm shows some errors in dmesg. Please
see: http://pastie.org/9877917