can't mount root disk with ACPI enabled

[Johannes Hofmann]

Sepherosa Ziehau <sepherosa at gmail.com> wrote:
>>
>> Just noticed that even with revision
>> 7e7d17cb48838b48389fb990950f2959b9635e63
>> I still can't mount the root disk iff I load usb modules (usb, ehci,
>> umass) during boot via /boot/loader.conf - which I normally don't to
>> allow CPU to enter C3 state.
> 
> You box is UP, so only i8254 is used.  C3 does not affect the i8254
> interrupt timer.

Right, but usb modules prevent the CPU from entering C3 generally 
(As far as I know it's a bus mastering DMA thing).

> 
>>
>> So maybe this is just some sort of timing problem?
>> Is anyone else seeing this? I guess thinkpads are quite common here.
> 
> This looks very strange, could you give me the bootverbose dmesgs:
> w/ ACPI, w/o usb modules

http://leaf.dragonflybsd.org/~hofmann/acpi_nousb.dmesg

> w/o ACPI, w/ usb modules

http://leaf.dragonflybsd.org/~hofmann/noacpi_usb.dmesg

> I think using these two combinition, your box is booting?

Exactly

> 
> BTW, what will happen if you load USB modules after boot?

That works fine.

Thanks,
Johannes