New i915drmkms startup hang

[Emmanuel Dreyfus <manu%netbsd.org@localhost>]

Hello

With new i915drmkms code, I often but not always get a hang at boot time.
Here are the relevant kernel threads when it happens:
PID    LID S CPU     FLAGS       STRUCT LWP *               NAME WAIT
1        1 3   2         0   ffffb71111cdd040               init lbolt
0      162 2   1       200   ffffb7111214c540          i915_flip
0      161 3   2       200   ffffb7111214c100       i915_modeset i915_modeset
0      160 3   2       200   ffffb71111e97940            i915-dp i915-dp
0       95 3   2       200   ffffb71111e97500               i915 i915
0    > 222 7   3       200   ffffb71111e970c0         configroot
0      221 3   0       200   ffffb71111c47580         configroot i915i2c

0.222 backtrace:
inl() at netbsd:inl+0x7
AcpiOsReadPciConfiguration() at netbsd:AcpiOsReadPciConfiguration+0x6b
AcpiEvAddressSpaceDispatch() at netbsd:AcpiEvAddressSpaceDispatch+0x12b
AcpiExAccessRegion() at netbsd:AcpiExAccessRegion+0x99
AcpiExFieldDatumIo() at netbsd:AcpiExFieldDatumIo+0x5e
AcpiExExtractFromFie~ld() at netbsd:AcpiExExtractFromField+0x88
AcpiExReadDataFromField() at netbsd:AcpiExReadDataFromField+0x97
AcpiExResolveNodeToValue() at netbsd:AcpiExResolveNodeToValue+0x228
AcpiDsEvaluateNamePath() at netbsd:AcpiDsEvaluateNamePath+0x8e
AcpiDsExecEndOp() at netbsd:AcpiDsExecEndOp+0x399
AcpiPsParseLoop() at netbsd:AcpiPsParseLoop+0xf4
AcpiPsParseAml() at netbsd:AcpiPsParseAml+0x181
AcpiPsExecuteMethod() at netbsd:AcpiPsExecuteMethod+0x13f
AcpiNsEvaluate() at netbsd:AcpiNsEvaluate+0x1fc
AcpiEvAsynchExecuteGpeMethod() at netbsd:AcpiEvAsynchExecuteGpeMethod+0xd5
sysmon_task_queue_thread() at netbsd:sysmon_task_queue_thread+0x87


0.162 backtrace:
_kernel_lock() at netbsd:_kernel_lock+0xc8
frag6_fasttimo() at netbsd:frag6_fasttimo+0x1a
pffasttimo() at netbsd:pffasttimo+0x34
callout_softclock() at netbsd:callout_softclock+0xbd
softint_dispatch() at netbsd:softint_dispatch+0xf9

Is it somehow a known problem? Should I fill a PR?
-- 
Emmanuel Dreyfus
manu%netbsd.org@localhost