psm0 isn't detected with acpi enabled

[Rahul Siddharthan]

On 5.1-BETA2 on a new machine (HP ZE5385US), with acpi enabled the
touchpad (psm0) isn't detected at all.  On the other hand, if I
disable acpi the machine doesn't boot fully, but hangs while mounting
the root FS, though I see psm0 in the messages scrolling by.

Any suggestions?  This seems similar to pr i386/49116, but that report
shows a message "psm0: unable to allocate irq" while in my case psm
doesn't show up at all in dmesg.

Thanks,
Rahul