Mailinglist Archive: opensuse-kernel (110 mails)

[Greg KH <gregkh@xxxxxxx>]

On Thu, Oct 20, 2011 at 03:59:32PM +0200, Guido Berhoerster wrote:
> * Greg KH <gregkh@xxxxxxx> [2011-10-20 15:37]:
> > On Thu, Oct 20, 2011 at 02:59:05PM +0200, Guido Berhoerster wrote:
> > > Hi,
> > > can anyone give me a rough estimation of the level of sysfs
> > > support for setting backlight brightness on common hardware
> > > compared to xrandr?
> >
> > They are two totally different things.
> >
> > > Basically, xfce4-power-manager has a bug in the xrandr backend
> > > making it crash on resume
> > > (https://bugzilla.novell.com/show_bug.cgi?id=707127,
> > > https://bugzilla.xfce.org/show_bug.cgi?id=7851) and since
> > > upstream is unresponsive I'm wondering what the cost/benefit of
> > > temporarily disabling the xrandr backend would be, ie. whether
> > > disabling the xrandr backend and relying exclusively on the sysfs
> > > backend would break brightness manipulation for a large number
> > > of users.
> >
> > xrandr should be using the sysfs interface the kernel exposes, if it is
> > present, otherwise, it might try to use some other interface, but it
> > should always be trying to use the sysfs one if it is there.
>
> Thanks for the explanation, x-p-m can instead of xrandr use a
> privileged helper binary to manipulate sysfs directly. How
> prevalent is the kernel support for manipulating brightness via
> sysfs (relative to any of the "other interfaces" xrandr might
> use)?

It all depends on the hardware involved, everything should be using the
kernel sysfs interface, but older hardware doesn't always have their
drivers updated, or for some older hardware, we don't have kernel
drivers to provide this interface.

greg k-h
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