[Intel-gfx] [PATCH] drm/i915: Fix eDP blank screen after S3 resume on HP desktops

[Takashi Iwai]

At Wed, 20 Jun 2012 10:05:12 +0200,
Daniel Vetter wrote:
> 
> On Wed, Jun 20, 2012 at 09:17:41AM +0200, Takashi Iwai wrote:
> > This patch fixes the problem on some HP desktop machines with eDP
> > which give blank screens after S3 resume.
> > 
> > The problem looks like a timing issue.  Although BLC_PWM_CPU_CTL
> > register is already restored at the beginning of resume, it doesn't
> > seem to take effect.  Simply re-issuing the  register write restores
> > the backlight gracefully.
> > 
> > Tested with 3.5-rc3 kernel.
> > 
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=49233
> > 
> > Signed-off-by: Takashi Iwai <tiwai at suse.de>
> 
> This patch looks very fishy as-is, simply because I don't like adding
> random calls to random functions at pretty much random places without any
> hint why it works.

It's difficult to know exactly why it works.  We can only guess, but
nothing more than that, just like between husband and wife :)

> Just a few weeks ago we've had tons of fun with writes
> that don't stick when the ring isn't yet set up. Can you please check with
> a bunch of printks what exactly happens to the value of BLC_PWM_CPU_CTL?
> I.e. whether the write doesn't stick or whether it gets reset somewhere
> between the register restore functions and the new place.

The register value is already set, and not touched after that.
I've already checked.

> I suspect the opregion_init call could allow the bios to frob with these
> registers. If that's the case, the patch is missing a comment that to that
> effect.

Right.  That's also my suspect.

> Essentially I want to know why this place here works and why not move the
> call a few lines up or down.

A few lines down works definitely.  Even just writing to sysfs works.
A few lines up, well, I need to check where is the border line.


Takashi

> -Daniel
> 
> > ---
> >  drivers/gpu/drm/i915/i915_drv.c |    3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> > index 9fe9ebe..2ba1350 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.c
> > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > @@ -658,6 +658,9 @@ static int i915_drm_thaw(struct drm_device *dev)
> >  
> >  	intel_opregion_init(dev);
> >  
> > +	if (dev_priv->backlight)
> > +		backlight_update_status(dev_priv->backlight);
> > +
> >  	dev_priv->modeset_on_lid = 0;
> >  
> >  	console_lock();
> > -- 
> > 1.7.10.4
> > 
> > _______________________________________________
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> > Intel-gfx at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Daniel Vetter
> Mail: daniel at ffwll.ch
> Mobile: +41 (0)79 365 57 48
>