[Bug 67813] [HSW bisected]igt/module_reload causes [drm:hsw_unclaimed_reg_check] *ERROR* Unclaimed write to 44004 and system hang with headless, with power well disabled

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=67813

--- Comment #17 from Paulo Zanoni <przanoni at gmail.com> ---
Ok, I reinstalled my OS and now I can reproduce the bug. I also did an
analysis:

The bug is not really caused by module reload, it's caused by the "echo 0 >
/sys/class/vtconsole/vtcon1/bind" command that's part of the module_reload
script.

Since I couldn't reproduce the bug in my previous installation, I suspect the
bug is dependent on which console driver is used.

We get the problem even if the power well is enabled when we run the command.
But if the power well was *never* disabled, we don't get the problem. This
means that the condition to make the bug happen later is just a disable/enable
cycle on the power well.

Another thing I notice is that the endless flood of "unclaimed register"
messages doesn't seem to be triggered by our driver. It seems something else is
causing these messages. Maybe something is writing to VGA memory?

If we disable the north display error interrupts, everything appears to work
(except for a few error messages on dmesg).

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