Stable kernel 3.8.3 appears to break displayport on intel gen4

[Bjørn Mork]

Sergio Callegari <sergio.callegari at gmail.com> writes:

> This is just a short note to let you know that after installing 3.8.3,
> display port stopped working on my laptop. Going back to 3.8.2 brought
> it back to life.
> This has been tested with the ubuntu mainline kernels that should be
> vanilla stable kernels. Hope this is not an incorrect report due to
> something wrong on their side. Laptop is a DELL E6500 with intel gen4
> integrated graphics (Intel Corporation Mobile 4 Series Chipset
> Integrated Graphics Controller (rev 07)).
> With 3.8.3, xrandr does not report anymore the external monitor when
> it is actually attached via displayport.

I can confirm seeing this bug on:

# lspci -nnvvvs 00:02.0
00:02.0 VGA compatible controller [0300]: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller [8086:2a42] (rev 07) (prog-if 00 [VGA controller])
        Subsystem: Lenovo Device [17aa:20e4]
        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 45
        Region 0: Memory at f0000000 (64-bit, non-prefetchable) [size=4M]
        Region 2: Memory at d0000000 (64-bit, prefetchable) [size=256M]
        Region 4: I/O ports at 1800 [size=8]
        Expansion ROM at <unassigned> [disabled]
        Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
                Address: fee0300c  Data: 4152
        Capabilities: [d0] Power Management version 3
                Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
                Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
        Kernel driver in use: i915



Looking through the changes from v3.8.2 to v3.8.3, there weren't really
that many suspects.  This partial (to avoid having to change any
following patches) revert of commit 2a98104 ("drm/i915: reorder setup
sequence to have irqs for output setup") fixes the problem for me.  I
have no idea why, so I leave it to Daniel and the other wise men working
on this driver to explain and cleanup :)


---
 drivers/gpu/drm/i915/i915_dma.c |   14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index 5206f24..b15b65d 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1297,21 +1297,19 @@ static int i915_load_modeset_init(struct drm_device *dev)
 	if (ret)
 		goto cleanup_vga_switcheroo;
 
-	ret = drm_irq_install(dev);
-	if (ret)
-		goto cleanup_gem_stolen;
-
-	/* Important: The output setup functions called by modeset_init need
-	 * working irqs for e.g. gmbus and dp aux transfers. */
 	intel_modeset_init(dev);
 
 	ret = i915_gem_init(dev);
 	if (ret)
-		goto cleanup_irq;
+		goto cleanup_gem_stolen;
+
+	intel_modeset_gem_init(dev);
 
 	INIT_WORK(&dev_priv->console_resume_work, intel_console_resume);
 
-	intel_modeset_gem_init(dev);
+	ret = drm_irq_install(dev);
+	if (ret)
+		goto cleanup_gem;
 
 	/* Always safe in the mode setting case. */
 	/* FIXME: do pre/post-mode set stuff in core KMS code */