linux-kernel - Regression in i915 in kernel 4.6.0-git

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Date:	Thu, 26 May 2016 17:11:42 -0500
From:	Larry Finger <Larry.Finger@...inger.net>
To:	Shubhangi Shrivastava <shubhangi.shrivastava@...el.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Daniel Vetter <daniel.vetter@...el.com>
Cc:	intel-gfx@...ts.freedesktop.org,
	DRI <dri-devel@...ts.freedesktop.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Regression in i915 in kernel 4.6.0-git - bisected to
 f21a21983ef13a031

The latest mainline kernel (commit 3f59de0) shows a regression. The symptom is 
that as soon as the kernel is started, the display is blanked, and it is never 
turned on again. This problem was bisected to commit 
f21a21983ef13a031250c4c3f6018e29a549d0f1
("drm/i915: Splitting intel_dp_detect"). The adapter in question is the 
integrated graphics controller on a Toshiba Tecra A50 laptop. The output of 
"lspci -nnv" for that controller is as follows:

00:02.0 VGA compatible controller [0300]: Intel Corporation 4th Gen Core 
Processor Integrated Graphics Controller [8086:0416] (rev 06) (prog-if 00 [VGA 
controller])
         Subsystem: Toshiba America Info Systems Device [1179:0002]
         Flags: bus master, fast devsel, latency 0, IRQ 27
         Memory at e0000000 (64-bit, non-prefetchable) [size=4M]
         Memory at d0000000 (64-bit, prefetchable) [size=256M]
         I/O ports at 4000 [size=64]
         Expansion ROM at <unassigned> [disabled]
         Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
         Capabilities: [d0] Power Management version 2
         Capabilities: [a4] PCI Advanced Features
         Kernel driver in use: i915
         Kernel modules: i915

If the kernel is booted with "nomodeset", the display is normal.

I will be happy to test any patches, or to answer any further questions.

Thanks,

Larry