Comment 585 for bug 1690085

OS: Antergos Linux 4.20.3-arch1-1-ARCH #1 SMP PREEMPT Wed Jan 16 22:38:58 UTC 2019 x86_64 GNU/Linux.
CPU: AMD Ryzen 7 1700 Eight-Core Processor.
CPU flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc cpuid extd_apicid aperfmperf pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 movbe popcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw skinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx cpb hw_pstate sme ssbd sev ibpb vmmcall fsgsbase bmi1 avx2 smep bmi2 rdseed adx smap clflushopt sha_ni xsaveopt xsavec xgetbv1 xsaves clzero irperf xsaveerptr arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif overflow_recov succor smca
MB: ASRock AB350 Gaming-ITX/ac; Version: P4.60; Release Date: 04/19/2018
RAM: F4-2400C15D-16GFXR, 32 GB DDR4.

Attempt #1:
a) Set BIOS / Advanced / AMD CBS / Zen Common Options / Power Supply Idle Control to "Typical Current Idle".

Result: Hangs

Attempt #2:
a) Set /etc/default/grub to: GRUB_CMDLINE_LINUX_DEFAULT="quiet idle=nomwait resume=UUID=9d2d2002-406a-4eb5-bd21-fdb889831991"
b) Ran update-grub
c) Rebooted
d) BIOS remains at "Typical Current Idle"

Result: Hangs

Journal Log:

Jan 24 17:21:00 kernel: BUG: unable to handle kernel paging request at ffffffffffffffff
Jan 24 17:21:00 kernel: PGD 3a0a0e067 P4D 3a0a0e067 PUD 3a0a10067 PMD 0
Jan 24 17:21:00 kernel: Oops: 0000 [#1] PREEMPT SMP NOPTI
Jan 24 17:21:00 kernel: CPU: 1 PID: 994 Comm: xfwm4 Not tainted 4.20.3-arch1-1-ARCH #1
Jan 24 17:21:00 kernel: Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./AB350 Gaming-ITX/ac, BIOS P4.60 04/19/2018
Jan 24 17:55:01 kernel: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
Jan 24 17:55:01 kernel: NMI watchdog: Watchdog detected hard LOCKUP on cpu 4
Jan 24 17:55:27 kernel: rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks:
Jan 24 17:59:39 kernel: ACPI BIOS Warning (bug): Optional FADT field Pm2ControlBlock has valid Length but zero Address: 0x0000000000000000/0x1 (20181003/tbfadt-624)
Jan 24 17:59:39 kernel: [Firmware Bug]: ACPI MWAIT C-state 0x0 not supported by HW (0x0)

$ sudo cat /boot/grub/grub.cfg | grep -i idle
 linux /vmlinuz-linux root=UUID=16a8e892-ec00-4316-b62d-5b60da84a7fb rw quiet idle=nomwait resume=UUID=9d2d2002-406a-4eb5-bd21-fdb889831991

Have not tried:

1) idle=halt
2) Disable C6 state with zenstates.py
3) BIOS upgrade