kern/50060: kernel crash with i915drmksm on Intel 965Q

[nisimura%netbsd.org@localhost]

>Number:         50060
>Category:       kern
>Synopsis:       kernel crash with i915drmksm on Intel 965Q
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Jul 18 01:30:01 +0000 2015
>Originator:     Toru Nishimura
>Release:        NetBSD 7.0_RC1
>Organization:
ALKYL Technology
>Environment:
NetBSD paq16 7.0_RC1 NetBSD 7.0_RC1 (GENERIC.201506190427Z) amd64
>Description:
From the introduction of i915drmkms hp dc7700 has never been successful to boot off since i915drmkms always crashs.

agp0 at pchb0: i965-family chipset
pci_mem_find: expected mem type 00000004, found 00000000
pci_mem find: expected mem type 00000004, found 00000000
agp0: can't find MMIO registers
i915drmksm0 at pci0 dev 2 function 0: vendor 0x8086 product 0x2992 (rev. 0x02)
DRM error in i915_gmch_probe: failed to set up gmch
uvm_fault(0xffffffff8104b240, 0x7fc000231000, 2) -> e
fatal page fault in supervisor mode
trap type 6 code 2 rip ffffffff809cb323 cs 8 rflags 10246 cr2 7fc000231000 ilevel 8 rsp ffffffff812657e8
curlwp 0xffffffff81000540 pid 0.1 lowest kstack ffffffff812632c0
kernel: page fault trap, code=0
Stopped in pid 0.1 (system) at  netbsd:_atomic_swap_64+0x3: xchgq %rax,0(%rdi)

- 6.1.5 which uses i915drm has no trouble so far.
- "boot -c / disable i915drmkms" is the only to avoid crash.
- hp dc7700 is pure Intel-Inside product, supposedly one of most standard desktop PC.

Toru Nishimura / ALKYL Technology
>How-To-Repeat:
Boot off off the shelf NetBSD7.0_RC1 kernel on 965Q system. Mine happens to have E6300/E6600 C2D.
>Fix: