IBM T42 freezes when going to sleep under X11

[Jacques Garrigue]

From: Jacques Garrigue <garrigue at math.nagoya-u.ac.jp>
> I've got a strange problem with my IBM T42 / Radeon M10 setup.
> 
> When using the 6.0-RELEASE kernel (including GENERIC), I cannot go to
> sleep when X11 is running: the machine freezes, display still on. I
> tried disabling DRI, but this does not seem to be the problem: I have
> no DRM anyway.
> 
> On the other hand, everything works fines with a 6.0-RC1 kernel.
> Was there a big change in between, such that I need to change my
> configuration?

I finally found the cause of my problems: there has been changes in
the em driver (Gb ethernet), such that the machine freezes when trying
to switch automatically from the X11 VT to the system console, before
going to sleep. The interaction is surprising, but clearly the problem
disappears when I remove "device em" from the kernel configuration,
and it reappears when I do "kldload if_em". Since I'm using only ath
(wireless) anyway, this is fine with me...

A previous partial solution suggested to me was to add
  hw.syscons.sc_no_suspend_vtswitch=1
to sysctl.conf, but this means the screen gets garbled and I have to
do the switch by hand anyway, which is a real pain.
Worse still: the machine would still freeze when going to sleep while
the disk is active.

The last step is to track down the bug in em, as it still seems to
be there in yesterday's STABLE.

Jacques Garrigue