Re: i915 regression on 3.6-rc1: lid blanks screen

[Takashi Iwai <tiwai@suse.de>]

At Mon, 6 Aug 2012 11:25:30 -0700 (PDT),
Hugh Dickins wrote:
> 
> On Mon, 6 Aug 2012, Daniel Vetter wrote:
> > On Mon, Aug 6, 2012 at 6:21 AM, Hugh Dickins <hughd@google.com> wrote:
> > > On Sun, 5 Aug 2012, Takashi Iwai wrote:
> > >> At Sat, 4 Aug 2012 10:01:13 -0700 (PDT),
> > >> Hugh Dickins wrote:
> > >> >
> > >> > Sorry to report that with 3.6-rc1, closing and opening the lid on
> > >> > this ThinkPad T420s leaves the screen blank, and I have to reboot.
> > >> >
> > >> > Bisection led to this commit, and reverting indeed gets my screen back:
> > >> >
> > >> > commit 520c41cf2fa029d1e8b923ac2026f96664f17c4b
> > >> > Author: Daniel Vetter <daniel.vetter@ffwll.ch>
> > >> > Date:   Wed Jul 11 16:27:52 2012 +0200
> > >> >
> > >> >     drm/i915/lvds: ditch ->prepare special case
> > > ...
> > >>
> > >> Hm, it's surprising.
> > >>
> > >> Could you check whether the counter-part intel_lvds_enable() is
> > >> called?  If the prepare callback affects, it must be from the mode
> > >> setting (drm_crtc_helper_set_mode()).
> > >
> > > Yes, I put a dump_stack() in both, and intel_lvds_enable() gets called
> > > about 0.28 seconds after the intel_lvds_disable() when I lift the lid;
> > > but with no video display until I revert that commit.
> > 
> > Can you please boot with drm.debug=0xe added to your kernel cmdline,
> > reproduce the issue (with the two dump_stack calls added) and then
> > attach the full dmesg?
> 
> Collected, I'll send it to you both privately in a moment.
> 
> > 
> > Also a few other things to try: What happens if you do a modeset on
> > the LVDS while it's still working, e.g.
> 
> In the dmesg, I've only gone to runlevel 3, simply working on the
> console without startx.  For these xrandrs to work, I did startx
> and used the graphics screen.

OK, now I can see the problem here, too.  The key is that it happens
only on Linux console, not on X.  That's why no one else reported.
I guess the problem can be seen on many laptops with LVDS on PCH.

Looking at intel_reg_dumper output, BLC_PWM_CPU_CTL is 0 while other
registers are set correctly.  This seems coming from the rewrite of 
backlight control code by commit
  24ded204: drm/i915: properly enable the blc controller on the right pipe
and
  a4f32fc3: drm/i915: don't forget the PCH backlight registers
    
While the latter fixes the regression by the former commit, it still
doesn't cover this regression.

I don't know the exact hardware behavior, but it looks like that
resetting BLC_PWM_PCH_CTL2 and BLC_PWM_PCH_CTL1 clears the
BLC_PWM_CPU_CTL (oh what confusing reg names).

FWIW, the commit 520c41cf you mentioned is no direct cause.  This
patch works fine on the top of 3.5 kernel.  But it's like a bad drug,
the combination of this and other two commits break things.

The patch below is my quick fix.  It worked on an HP laptop.
Hugh, could you give it a try?


thanks,

Takashi

===
From: Takashi Iwai <tiwai@suse.de>
Subject: [PATCH] drm/i915: Fix blank panel at reopening lid on Linux console

When you reopen the lid on Linux console on a laptop with PCH, the
panel suddenly goes blank.  It seems because BLC_PWM_CPU_CTL register
is cleared when BLC_PWM_PCH_CTL1 and BLC_PWM_PCH_CTL2 registers are
played.

This patch fixes the problem by setting BLC_PWM_CPU_CTL after enabling
BLC_PWM_PCH_CTL_1 and _2 registers.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 drivers/gpu/drm/i915/intel_panel.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 10c7d39..d640425 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -311,9 +311,6 @@ void intel_panel_enable_backlight(struct drm_device *dev,
 	if (dev_priv->backlight_level == 0)
 		dev_priv->backlight_level = intel_panel_get_max_backlight(dev);
 
-	dev_priv->backlight_enabled = true;
-	intel_panel_actually_set_backlight(dev, dev_priv->backlight_level);
-
 	if (INTEL_INFO(dev)->gen >= 4) {
 		uint32_t reg, tmp;
 
@@ -326,7 +323,7 @@ void intel_panel_enable_backlight(struct drm_device *dev,
 		 * we don't track the backlight dpms state, hence check whether
 		 * we have to do anything first. */
 		if (tmp & BLM_PWM_ENABLE)
-			return;
+			goto set_level;
 
 		if (dev_priv->num_pipe == 3)
 			tmp &= ~BLM_PIPE_SELECT_IVB;
@@ -347,6 +344,10 @@ void intel_panel_enable_backlight(struct drm_device *dev,
 			I915_WRITE(BLC_PWM_PCH_CTL1, tmp);
 		}
 	}
+
+set_level:
+	dev_priv->backlight_enabled = true;
+	intel_panel_actually_set_backlight(dev, dev_priv->backlight_level);
 }
 
 static void intel_panel_init_backlight(struct drm_device *dev)
-- 
1.7.11.4