[Intel-gfx] BACKLIGHT property for KMS case
jbarnes at virtuousgeek.org
Tue Aug 18 09:25:26 PDT 2009
On Tue, 18 Aug 2009 11:07:08 +0800
ykzhao <yakui.zhao at intel.com> wrote:
> The two boxes are based on the g4x platform. And the acpi backlight
> interface can work well on one box. And there is no acpi backlight
> interface on another box.
> In fact I check the vbios dump on several other boxes and the length
> of backlight section is 21. So IMO the backlight section is not
> reliable and we can't use it to parse the backlight interface.
None of the VBIOS dumps I have seem to have this sort of corruption;
most have a length of 97, which is correct given the size of the
backlight info struct we're using. But like I said, on 965+ platforms
it doesn't matter, since they'll have OpRegion support (they're
required to afaik).
> > > Another issue is that the brightness level is so big when the
> > > native/combo mode is used. For example: 0-65535 for the native
> > > control method. The user will be confused by so many brightness
> > > levels.
> > User won't see them directly, so there should be no confusion.
> > Brightness is generally exposed as a slider or a series of steps
> > with the brightness keys.
> But this interface can be found in /sys/class/backlight/*. Maybe it is
> used to adjust the brightness by user. In such case too many
> brightness levels are exposed to user.
If the user is poking /sys/class/backlight directly, they should be
technical enough to not be confused by large numbers.
> > > How about using the legacy control method?
> > Yes, we have to modify the legacy registers in some cases. But
> > modifying them exclusively would be a problem...
> How can we modify the legacy registers in the two different paths if
> we expose only one interface to user space?
If the legacy registers are active, they'll usually be used by firmware
code to adjust the backlight quickly & easily. If the firmware adjusts
them to 0, we may have to increase the value when we get a request
through the backlight interface we export, or the brightness will
remain at 0. In most other cases we'll only adjust the PWM value.
Jesse Barnes, Intel Open Source Technology Center
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