Xorg framebuffer and brightness of screen

[Alex Deucher]

On Fri, Nov 12, 2021 at 11:21 PM Riza Dindir <riza.dindir at gmail.com> wrote:
>
> Hello Alex,
>
> Isn't there a software based solution to set the brightness in xorg?

Not really.  You need some interface to talk to the backlight
controller, either via software via a driver or via some firmware
interface like ACPI if the platform supports it.  You can also adjust
the gamma on the display which will give the perception of changes in
brightness, but it won't actually change the levels of the backlight
itself.  That said, you need driver support to adjust the gamma as
well.

Alex

>
> Riza
>
> On Fri, Nov 12, 2021 at 11:37 PM Alex Deucher <alexdeucher at gmail.com> wrote:
> >
> > On Fri, Nov 12, 2021 at 12:36 AM Riza Dindir <riza.dindir at gmail.com> wrote:
> > >
> > > Hello Ken.
> > >
> > > On Fri, Nov 12, 2021 at 12:56 AM Ken Moffat <zarniwhoop at ntlworld.com> wrote:
> > > >
> > > > On Thu, Nov 11, 2021 at 10:16:18AM +0300, Riza Dindir wrote:
> > > > > Hello Ken
> > > > >
> > > > > I am using gop, and a framebuffer. When i try to use the xrandr, it says
> > > > > "gamma is set to 0", or "failed to get size of gamma for output default".
> > > > >
> > > > > I can set the gamma uaing xgamma and in the xorg.conf file.
> > > > >
> > > > > Riza
> > > > >
> > > > No idea what gop is - google suggests it's the american republican
> > > > party ;-)
> > >
> > > :D That is the graphics output protocol.
> > >
> > > My radeon device is not recognized by the kernel (netbsd) and I am
> > > using a framebuffer.
> > >
> > > >
> > > > Did you search for that "failed to get" message ?  Google gives me a lot of
> > > > different matches, some for failing to correctly add a new mode,
> > > > others for running with nvidia drivers or in virtualbox, or with out
> > > > of date manufacturer's video driver.
> > > > https://askubuntu.com/questions/441040/failed-to-get-size-of-gamma-for-output-default-when-trying-to-add-new-screen-res
> > > >
> > > > For an ubuntu-based kernel with at-the-time recent intel graphics
> > > > hardware, adding a boot arg to enable alpha-quality intel support.
> > > > https://itectec.com/ubuntu/ubuntu-xrandr-failed-to-get-size-of-gamma-for-output-default-for-mdp-type-connection/
> > > >
> > > > In short, finding the answer really does seem to depend on what
> > > > hardware and distro are in use.  I'm assuming you're using some sort
> > > > of linux.
> > >
> > > What I am trying to do is reduce the brightness of the LCD on my
> > > laptop. Since I am using a framebuffer, I thought that I could do that
> > > with the gamma values. But xrandr fails with  a message relating to
> > > the gamma values being 0 or not set.
> >
> > You might get lucky if your system supports backlight control via
> > hotkeys or some ACPI interface which your BSD supports.  If not, then
> > not.  There's no backlight control in GOP.
> >
> > Alex
> >
> >
> > >
> > > >
> > > > ĸen
> > > > --
> > > > Vetinari smiled. "Can you keep a secret, Mister Lipwig?"
> > > > "Oh, yes, sir. I've kept lots."
> > > > "Capital. And the point is, so can I. You do not need to know.”
> > >
> > > Regards,
> > > Riza