mt8173-evb: failing to boot in linux-next and mainline

[Kevin Hilman]

Hello,

The mt8173-evb has been failing to boot in linux-next since 29 Feb,
and is now causing failures in mainline[2] since the merge window is
open and things are getting merged.

Bisecting this has led to inconclusive results, so I'm still not sure
what the real culprit is.  The last few kernel for the failures are:

[    0.570979] NET: Registered protocol family 17
[    0.571615] 9pnet: Installing 9P2000 support
[    0.572211] Key type dns_resolver registered
[    0.573195] registered taskstats version 1
[    0.574170] hctosys: unable to open rtc device (rtc0)
[    0.581122] usb_vbus: disabling

Thinking it was this regulator getting prematurely disabled, I set the
'regulator-always-on' property, which doesn't do much better, but does
report a CPU stall:

[    0.556186] NET: Registered protocol family 17
[    0.556829] 9pnet: Installing 9P2000 support
[    0.557496] Key type dns_resolver registered
[    0.558669] registered taskstats version 1
[    0.559611] hctosys: unable to open rtc device (rtc0)
[   21.573504] INFO: rcu_preempt detected stalls on CPUs/tasks:
[   21.574227]  1-...: (1 GPs behind) idle=483/140000000000000/0
softirq=221/222 fqs=2638
[   21.575227]  (detected by 3, t=5252 jiffies, g=-238, c=-239, q=204)
[   21.576017] Task dump for CPU 1:
[   21.576424] swapper/0       R  running task        0     1      0 0x00000002
[   21.577316] Call trace:
[   21.577634] [<ffffff8008086c20>] __switch_to+0xd0/0xdc
[   21.578280] [<ffffffc077096900>] 0xffffffc077096900
[   33.321443] random: nonblocking pool is initialized
[   84.593487] INFO: rcu_preempt detected stalls on CPUs/tasks:
[   84.594207]  1-...: (1 GPs behind) idle=483/140000000000000/0
softirq=221/222 fqs=10861
[   84.595216]  (detected by 3, t=21007 jiffies, g=-238, c=-239, q=204)
[   84.596017] Task dump for CPU 1:
[   84.596424] swapper/0       R  running task        0     1      0 0x00000002
[   84.597315] Call trace:
[   84.597628] [<ffffff8008086c20>] __switch_to+0xd0/0xdc
[   84.598273] [<ffffffc077096900>] 0xffffffc077096900

Anyways, I gave up on this for now hoping someone here would take a closer look.

Thanks,

Kevin

[1] https://kernelci.org/boot/mt8173-evb/job/next/kernel/next-20160324/defconfig/defconfig/lab/lab-khilman/?_id=56f3b10759b51423934b0500
[2] https://kernelci.org/boot/mt8173-evb/job/mainline/kernel/v4.5-12149-gaca04ce5dbda/defconfig/defconfig/lab/lab-khilman/?_id=56f3c33f59b5145aa14b04f2