[Intel-gfx] 282dbf9b "drm/i915: Pass intel_plane and intel_crtc to plane hooks" breaks i945GM in 4.13 and above

[Karl-Johan Karlsson]

Hello,

I have an old Lenovo Thinkpad X60 laptop with a Core 2 Duo T7200 CPU and 
i945GM integrated graphics whose graphics broke when I tried to update the 
kernel to get the Meltdown fixes.

GRUB2 shows a graphical boot menu, and Linux displays the Tux boot logos 
correctly at first. However, almost immediately after displaying the Tuxes, 
the actively scrolling area of the display shifts about two text lines 
downward, so that two decapitated penguin heads are left at the top of the 
screen and new text appears below the lower edge of the screen. When X starts, 
it too is shifted down the same amount, and only shows a black screen with a 
(working) mouse cursor. My display manager (SDDM) never shows up. Sometimes, 
while X is running, random pixels appear in the non-active area at the top of 
the screen containing the decapitated penguin heads.

My hardware is:

$ grep name /proc/cpuinfo
model name      : Intel(R) Core(TM)2 CPU         T7200  @ 2.00GHz
model name      : Intel(R) Core(TM)2 CPU         T7200  @ 2.00GHz

# lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation Mobile 945GM/GMS, 
943/940GML Express Integrated Graphics Controller (rev 03)

# grep Chipset: /var/log/Xorg.0.log
[    33.085] (--) intel(0): Integrated Graphics Chipset: Intel(R) 945GM

$ xrandr | grep primary
LVDS1 connected primary 1024x768+0+0 (normal left inverted right x axis y 
axis) 250mm x 180mm

Kernel 4.12.14 does not have the bug. 4.13 and 4.14.11 have the bug in console 
and X mode. 4.15-rc7 has the bug in console mode, but crashes (completely 
black screen, Magic SysRq to reboot is the only thing that works) when 
starting X.

Bisecting from 4.12 to 4.13 pointed to this as the first bad commit:

commit 282dbf9b017bc6d5fdaeadf14e534c2fe22fee2d
Author: Ville Syrjälä <ville.syrjala at linux.intel.com>
Date:   Mon Mar 27 21:55:33 2017 +0300

    drm/i915: Pass intel_plane and intel_crtc to plane hooks

But I know nothing about the driver internals to explain why.

-- 
Karl-Johan Karlsson
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