linux-kernel - i915 regression on 3.6-rc1: lid blanks screen

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Date:	Sat, 4 Aug 2012 10:01:13 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Daniel Vetter <daniel.vetter@...ll.ch>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Chris Wilson <chris@...is-wilson.co.uk>,
	Takashi Iwai <tiwai@...e.de>, Giacomo Comes <comes@...c.edu>,
	linux-kernel@...r.kernel.org
Subject: i915 regression on 3.6-rc1: lid blanks screen

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.

I understand there's also an nVidia graphics device in here,
but I have that configured out, preferring to use the i915:

00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09) (prog-if 00 [VGA controller])
	Subsystem: Lenovo Device 21d3
	Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
	Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
	Latency: 0
	Interrupt: pin A routed to IRQ 41
	Region 0: Memory at f1400000 (64-bit, non-prefetchable) [size=4M]
	Region 2: Memory at e0000000 (64-bit, prefetchable) [size=256M]
	Region 4: I/O ports at 5000 [size=64]
	Expansion ROM at <unassigned> [disabled]
	Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
		Address: fee0100c  Data: 41c2
	Capabilities: [d0] Power Management version 2
		Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
		Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
	Capabilities: [a4] PCI Advanced Features
		AFCap: TP+ FLR+
		AFCtrl: FLR-
		AFStatus: TP-
	Kernel driver in use: i915

Bisection led to this commit, and reverting indeed gets my screen back:

commit 520c41cf2fa029d1e8b923ac2026f96664f17c4b
Author: Daniel Vetter <daniel.vetter@...ll.ch>
Date:   Wed Jul 11 16:27:52 2012 +0200

    drm/i915/lvds: ditch ->prepare special case
    
    LVDS is the first output where dpms on/off and prepare/commit don't
    perfectly match. Now the idea behind this special case seems to be
    that for simple resolution changes on the LVDS we don't need to stop
    the pipe, because (at least on newer chips) we can adjust the panel
    fitter on the fly.
    
    There are a few problems with the current code though:
    - We still stop and restart the pipe unconditionally, because the crtc
      helper code isn't flexible enough.
    - We show some ugly flickering, especially when changing crtcs (this
      the crtc helper would actually take into account, but we don't
      implement the encoder->get_crtc callback required to make this work
      properly).
    
    So it doesn't even work as advertised. I agree that it would be nice
    to do resolution changes on LVDS (and also eDP) whithout blacking the
    screen where the panel fitter allows to do that. But imo we should
    implement this as a special case a few layers up in the mode set code,
    akin to how we already detect simple framebuffer changes (and only
    update the required registers with ->mode_set_base).
    
    Until this is all in place, make our lives easier and just rip it out.
    
    Also note that this seems to fix actual bugs with enabling the lvds
    output, see:
    
    http://lists.freedesktop.org/archives/intel-gfx/2012-July/018614.html
    
    Cc: Takashi Iwai <tiwai@...e.de>
    Cc: Giacomo Comes <comes@...c.edu>
    Acked-by: Chris Wilson <chris@...is-wilson.co.uk>
    Tested-by: Takashi Iwai <tiwai@...e.de>
    Signed-Off-by: Daniel Vetter <daniel.vetter@...ll.ch>

diff --git a/drivers/gpu/drm/i915/intel_lvds.c b/drivers/gpu/drm/i915/intel_lvds.c
index 49f09a8..e05c0d3 100644
--- a/drivers/gpu/drm/i915/intel_lvds.c
+++ b/drivers/gpu/drm/i915/intel_lvds.c
@@ -409,13 +409,7 @@ static void intel_lvds_prepare(struct drm_encoder *encoder)
 {
 	struct intel_lvds *intel_lvds = to_intel_lvds(encoder);
 
-	/*
-	 * Prior to Ironlake, we must disable the pipe if we want to adjust
-	 * the panel fitter. However at all other times we can just reset
-	 * the registers regardless.
-	 */
-	if (!HAS_PCH_SPLIT(encoder->dev) && intel_lvds->pfit_dirty)
-		intel_lvds_disable(intel_lvds);
+	intel_lvds_disable(intel_lvds);
 }
 
 static void intel_lvds_commit(struct drm_encoder *encoder)
--
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