i915 regression on 3.6-rc1: lid blanks screen

From: Hugh Dickins
Date: Sat Aug 04 2012 - 13:01:58 EST


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@xxxxxxxx>
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@xxxxxxx>
Cc: Giacomo Comes <comes@xxxxxxxx>
Acked-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Tested-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-Off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>

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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