8254 timer woes

["Simon 'corecode' Schubert" <corecode@xxxxxxxxxxxx>]

Hey,

I'm wondering... did we yet find a way to prevent bios calls from 
trashing our timer? Currently XOrg is freezing my machine (VIA EPIA 
M10k) when via_drv init reads the VBE EDID. Sure, I could just disable 
that, but a more clean solution would be to fix this situation.

Short info what happens: system freezes (a little bit) delayed (at 
least so it seems) when XOrg/via_drv/vbe calls int 
0x10/ax=0x4f15/bx=0x01/cx=0x0. I disassembled bits of the VGA BIOS (VGA 
is a integrated VIA CLE266 unichrome chipset), and it does, besides 
spooky register handling, set i8254 time counter 2 to divisor 0x4a9, 
i.e. 1kHz (if I'm not wrong) and then busy loops for a certain time.

Freezing my system means: nothing works any more, I can only break to 
ddb (if I'm lucky). Time freezes (for DragonFly): nanouptime() always 
reports the same. calling timer_restore() from ddb/gdb fixes 
everything: X starts as desired and system works again.

Problem here is that the system completely freezes and not "just" has 
funny time. The cause of this is that the VGA BIOS (card is an 
integrated VIA CLE266 unichrome) disables the timer 2 gate. A 
hackaround for me would be to (unconditionally) set the gate bit in 
cputimer_count(), but that can't be the real solution.

Is is possible to fault on special port IO so that we can prevent 
legacy BIOS/programs to destroy our timing?

cheers
  simon

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