[Intel-gfx] [RFT] drm/i915: enable/disable LVDS port at DPMS time

[Jesse Barnes]

On Fri, 12 Feb 2010 11:14:50 +0800
Zhenyu Wang <zhenyuw at linux.intel.com> wrote:

> On 2010.02.11 17:44:36 -0800, Jesse Barnes wrote:
> > > On Fri, 2010-02-12 at 04:41 +0800, Jesse Barnes wrote:
> > > > It would be good to disable the LVDS port when we shut down the
> > > > panel to save power.  We haven't done so until now because we
> > > > had trouble getting the right LVDS parameters from the BIOS.  I
> > > > think we're past that now, so enabling and disabling the port
> > > > should be safe, though it would probably be made cleaner with
> > > > some additional changes to the display code, where we also bang
> > > > on the LVDS reg to set the pairing correctly etc.
> > > > 
> > > > Seems to save a bit of power (up to 300mW in my basic wattsup
> > > > meter testing).
> > > 
> > > Hi, Jesse
> > >     Do you test it on the laptop based on Ironlake or
> > > crestline/cantiga platform?
> > >     
> > >     On the ironlake the LVDS_PORT_EN bit will be enabled/disabled
> > > in course of CRTC DPMS.
> > > 
> > > >From the spec this bit must be set before the display PLL is
> > > >enabled. 
> > 
> > Ah right, looks like on Ironlake we disable it there too, so this
> > patch isn't needed on Ironlake and above.
> > 
> 
> yeah, some order is required told by the spec, maybe applied to older
> mobile chips too? I haven't checked that out, but this is good thing
> to have for them, hopefully we can do more testing.

Yeah I ran into trouble when I just let intel_display.c enable LVDS,
since when turning on the panel it has to be enabled as well.  So I
think this is safe, but I'd like to figure out a way to do it in a more
obvious way...

-- 
Jesse Barnes, Intel Open Source Technology Center