[Intel-gfx] setting brightness with xrandr seem wrong

[Jani Nikula]

On Mon, 09 Dec 2013, zaverel <zaverel at free.fr> wrote:
> is it normal that if I rule the brightness with xrandr, only the value 
> of gamma change and not the brightness ?
>
> display actually becomes much clearer but this is due to gamma or 
> brightness ?
> That is the question.

Quoting xrandr(1) man page:

       --brightness brightness
              Multiply  the gamma values on the crtc currently attached to the
              output to specified floating value. Useful for overly bright  or
              overly  dim outputs.  However, this is a software only modifica‐
              tion, if your  hardware  has  support  to  actually  change  the
              brightness, you will probably prefer to use xbacklight.

Try 'xrandr --verbose' or 'xbacklight -get' to see if you have outputs
with backlight control support; this is usually the case for local flat
panels such as eDP or LVDS only.

BR,
Jani.


>
> Thanks.
> See you.
>
>
> xrandr  --output HDMI2 --brightness 1.20
>
> xrandr --verbose report:
>
> ...
> HDMI2 connected 1920x1080+0+0 (0x4a) normal (normal left inverted right 
> x axis y axis) 160mm x 90mm
>          Identifier: 0x46
>          Timestamp:  1071203
>          Subpixel:   unknown
>          Gamma:      0.75:0.75:0.75
>          Brightness: 1.0
>          Clones:
>          CRTC:       1
>          CRTCs:      0 1 2
>          Transform:  1.000000 0.000000 0.000000
>                      0.000000 1.000000 0.000000
>                      0.000000 0.000000 1.000000
>                     filter:
> ...
>
>
> I use latest xf86-video-intel devel from today
> xrandr 1.4.1
> kernel 3.12.4
>
>
>
>
> lspci -vxxx -s 0:02.0
>
> 00:02.0 VGA compatible controller: Intel Corporation Xeon E3-1200 v2/3rd 
> Gen Core processor Graphics Controller (rev 09) (prog-if 00 [VGA 
> controller])
>          Subsystem: Micro-Star International Co., Ltd. Device 2111
>          Flags: bus master, fast devsel, latency 0, IRQ 43
>          Memory at f7800000 (64-bit, non-prefetchable) [size=4M]
>          Memory at e0000000 (64-bit, prefetchable) [size=256M]
>          I/O ports at f000 [size=64]
>          Expansion ROM at <unassigned> [disabled]
>          Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
>          Capabilities: [d0] Power Management version 2
>          Capabilities: [a4] PCI Advanced Features
>          Kernel driver in use: i915
>          Kernel modules: i915
> 00: 86 80 52 01 07 04 90 00 09 00 00 03 00 00 00 00
> 10: 04 00 80 f7 00 00 00 00 0c 00 00 e0 00 00 00 00
> 20: 01 f0 00 00 00 00 00 00 00 00 00 00 62 14 11 21
> 30: 00 00 00 00 90 00 00 00 00 00 00 00 0b 01 00 00
> 40: 09 00 0c 01 92 80 80 e2 d0 00 50 14 00 00 00 00
> 50: 41 02 00 00 11 00 00 00 00 00 00 00 01 00 a0 cf
> 60: 00 00 02 00 00 00 00 00 00 00 00 00 00 00 00 00
> 70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 90: 05 d0 01 00 0c f0 e0 fe c1 41 00 00 00 00 00 00
> a0: 00 00 00 00 13 00 06 03 00 00 00 00 00 00 00 00
> b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> d0: 01 a4 22 00 00 00 00 00 00 00 00 00 00 00 00 00
> e0: 00 00 00 00 00 00 00 00 00 80 00 00 00 00 00 00
> f0: 00 00 00 00 00 00 00 00 00 00 09 00 18 60 43 cd
>
>
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-- 
Jani Nikula, Intel Open Source Technology Center