Also affects me, after idling for some time computer is taking a very long time to come back to life.

AMD Ryzen 7 1700
AMD RX550

[ 6380.343388] [drm:generic_reg_wait [amdgpu]] *ERROR* REG_WAIT timeout 10us * 3000 tries - dce110_stream_encoder_dp_blank line:927
[ 6380.343515] WARNING: CPU: 1 PID: 1830 at drivers/gpu/drm/amd/amdgpu/../display/dc/dc_helper.c:254 generic_reg_wait+0xe4/0x160 [amdgpu]
[ 6380.343516] Modules linked in: ipt_MASQUERADE nfnetlink xfrm_user xfrm_algo iptable_nat nf_nat_ipv4 overlay aufs nls_iso8859_1 usblp edac_mce_amd snd_hda_codec_realtek kvm_amd snd_hda_codec_generic snd_hda_codec_hdmi kvm snd_hda_intel snd_hda_codec irqbypass crct10dif_pclmul snd_hda_core crc32_pclmul snd_hwdep ghash_clmulni_intel pcbc snd_pcm aesni_intel snd_seq_midi snd_seq_midi_event aes_x86_64 crypto_simd snd_rawmidi cryptd joydev input_leds glue_helper snd_seq eeepc_wmi asus_wmi snd_seq_device sparse_keymap snd_timer video wmi_bmof snd k10temp soundcore ccp mac_hid ip6t_REJECT nf_reject_ipv6 nf_log_ipv6 xt_hl ip6t_rt nf_conntrack_ipv6 nf_defrag_ipv6 ipt_REJECT nf_reject_ipv4 nf_log_ipv4 nf_log_common xt_LOG xt_limit xt_tcpudp xt_addrtype nf_conntrack_ipv4 sch_fq_codel nf_defrag_ipv4 xt_conntrack
[ 6380.343560]  ip6table_filter ip6_tables br_netfilter bridge nf_conntrack_netbios_ns nf_conntrack_broadcast stp nf_nat_ftp llc nf_nat arp_tables nf_conntrack_ftp parport_pc nf_conntrack ppdev libcrc32c iptable_filter lp bpfilter parport ip_tables x_tables autofs4 hid_generic usbhid hid amdkfd amd_iommu_v2 amdgpu chash gpu_sched i2c_algo_bit ttm drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops uas usb_storage drm r8169 i2c_piix4 ahci mii libahci wmi gpio_amdpt gpio_generic
[ 6380.343596] CPU: 1 PID: 1830 Comm: Xorg Tainted: G        W         4.18.0-16-generic #17-Ubuntu
[ 6380.343597] Hardware name: System manufacturer System Product Name/PRIME B350M-A, BIOS 0806 07/12/2017
[ 6380.343681] RIP: 0010:generic_reg_wait+0xe4/0x160 [amdgpu]
[ 6380.343681] Code: a9 44 8b 45 20 48 8b 4d 18 89 de 44 89 4d d4 8b 55 10 48 c7 c7 10 d4 6f c0 e8 58 c7 da ff 41 83 7c 24 20 01 44 8b 4d d4 74 02 <0f> 0b 48 83 c4 18 44 89 c8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 41 0f 
[ 6380.343719] RSP: 0018:ffffa427423476e8 EFLAGS: 00010297
[ 6380.343721] RAX: 0000000000000000 RBX: 000000000000000a RCX: 0000000000000000
[ 6380.343723] RDX: 0000000000000000 RSI: ffff9212ce6564b8 RDI: ffff9212ce6564b8
[ 6380.343724] RBP: ffffa42742347728 R08: 0000000000053d5c R09: 0000000000010200
[ 6380.343726] R10: 0000000000000004 R11: ffffffffbb58880d R12: ffff9212cbc83e80
[ 6380.343727] R13: 0000000000000bb9 R14: 0000000000010000 R15: 0000000000000000
[ 6380.343730] FS:  00007f7534b31a80(0000) GS:ffff9212ce640000(0000) knlGS:0000000000000000
[ 6380.343731] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 6380.343733] CR2: 00007f529c4f17e0 CR3: 0000000407850000 CR4: 00000000003406e0
[ 6380.343734] Call Trace:
[ 6380.343831]  dce110_stream_encoder_dp_blank+0x12f/0x1a0 [amdgpu]
[ 6380.343918]  dce110_blank_stream+0x57/0x90 [amdgpu]
[ 6380.344003]  core_link_disable_stream+0x57/0x220 [amdgpu]
[ 6380.344087]  dce110_reset_hw_ctx_wrap+0xcd/0x1e0 [amdgpu]
[ 6380.344172]  dce110_apply_ctx_to_hw+0x52/0xa30 [amdgpu]
[ 6380.344257]  ? dce110_apply_ctx_for_surface+0x1f2/0x270 [amdgpu]
[ 6380.344340]  dc_commit_state+0x306/0x5b0 [amdgpu]
[ 6380.344421]  ? dc_stream_get_vblank_counter+0x57/0x60 [amdgpu]
[ 6380.344502]  ? mod_freesync_set_user_enable+0x11c/0x150 [amdgpu]
[ 6380.344593]  amdgpu_dm_atomic_commit_tail+0x395/0xe80 [amdgpu]
[ 6380.344599]  ? _cond_resched+0x19/0x30
[ 6380.344602]  ? wait_for_completion_timeout+0x38/0x140
[ 6380.344605]  ? _cond_resched+0x19/0x30
[ 6380.344608]  ? wait_for_completion_interruptible+0x35/0x1a0
[ 6380.344620]  commit_tail+0x42/0x70 [drm_kms_helper]
[ 6380.344632]  drm_atomic_helper_commit+0x113/0x120 [drm_kms_helper]
[ 6380.344723]  amdgpu_dm_atomic_commit+0x8d/0xa0 [amdgpu]
[ 6380.344746]  drm_atomic_commit+0x4a/0x50 [drm]
[ 6380.344757]  drm_atomic_helper_set_config+0x87/0x90 [drm_kms_helper]
[ 6380.344777]  __drm_mode_set_config_internal+0x6b/0x120 [drm]
[ 6380.344797]  drm_mode_setcrtc+0x71a/0x740 [drm]
[ 6380.344819]  ? drm_mode_connector_set_obj_prop+0x90/0x90 [drm]
[ 6380.344839]  ? drm_mode_getcrtc+0x190/0x190 [drm]
[ 6380.344857]  drm_ioctl_kernel+0xa4/0xf0 [drm]
[ 6380.344875]  drm_ioctl+0x227/0x400 [drm]
[ 6380.344894]  ? drm_mode_getcrtc+0x190/0x190 [drm]
[ 6380.344961]  amdgpu_drm_ioctl+0x4f/0x90 [amdgpu]
[ 6380.344966]  do_vfs_ioctl+0xa8/0x620
[ 6380.344970]  ksys_ioctl+0x67/0x90
[ 6380.344973]  __x64_sys_ioctl+0x1a/0x20
[ 6380.344978]  do_syscall_64+0x5a/0x110
[ 6380.344981]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 6380.344983] RIP: 0033:0x7f7535e683c7
[ 6380.344984] Code: 00 00 90 48 8b 05 c9 3a 0d 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 99 3a 0d 00 f7 d8 64 89 01 48 
[ 6380.345021] RSP: 002b:00007ffc8c5ffc78 EFLAGS: 00003246 ORIG_RAX: 0000000000000010
[ 6380.345023] RAX: ffffffffffffffda RBX: 00007ffc8c5ffcb0 RCX: 00007f7535e683c7
[ 6380.345025] RDX: 00007ffc8c5ffcb0 RSI: 00000000c06864a2 RDI: 000000000000000d
[ 6380.345026] RBP: 00007ffc8c5ffcb0 R08: 0000000000000000 R09: 000055cb72194d10
[ 6380.345027] R10: 00007ffc8c5ffd70 R11: 0000000000003246 R12: 00000000c06864a2
[ 6380.345028] R13: 000000000000000d R14: 0000000000000000 R15: 000055cb72194d10
[ 6380.345032] ---[ end trace 3753b196b455082b ]---
[ 6380.977073] [drm:generic_reg_wait [amdgpu]] *ERROR* REG_WAIT timeout 10us * 3000 tries - dce110_stream_encoder_dp_blank line:927
[ 6380.977190] WARNING: CPU: 2 PID: 1830 at drivers/gpu/drm/amd/amdgpu/../display/dc/dc_helper.c:254 generic_reg_wait+0xe4/0x160 [amdgpu]
[ 6380.977191] Modules linked in: ipt_MASQUERADE nfnetlink xfrm_user xfrm_algo iptable_nat nf_nat_ipv4 overlay aufs nls_iso8859_1 usblp edac_mce_amd snd_hda_codec_realtek kvm_amd snd_hda_codec_generic snd_hda_codec_hdmi kvm snd_hda_intel snd_hda_codec irqbypass crct10dif_pclmul snd_hda_core crc32_pclmul snd_hwdep ghash_clmulni_intel pcbc snd_pcm aesni_intel snd_seq_midi snd_seq_midi_event aes_x86_64 crypto_simd snd_rawmidi cryptd joydev input_leds glue_helper snd_seq eeepc_wmi asus_wmi snd_seq_device sparse_keymap snd_timer video wmi_bmof snd k10temp soundcore ccp mac_hid ip6t_REJECT nf_reject_ipv6 nf_log_ipv6 xt_hl ip6t_rt nf_conntrack_ipv6 nf_defrag_ipv6 ipt_REJECT nf_reject_ipv4 nf_log_ipv4 nf_log_common xt_LOG xt_limit xt_tcpudp xt_addrtype nf_conntrack_ipv4 sch_fq_codel nf_defrag_ipv4 xt_conntrack
[ 6380.977232]  ip6table_filter ip6_tables br_netfilter bridge nf_conntrack_netbios_ns nf_conntrack_broadcast stp nf_nat_ftp llc nf_nat arp_tables nf_conntrack_ftp parport_pc nf_conntrack ppdev libcrc32c iptable_filter lp bpfilter parport ip_tables x_tables autofs4 hid_generic usbhid hid amdkfd amd_iommu_v2 amdgpu chash gpu_sched i2c_algo_bit ttm drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops uas usb_storage drm r8169 i2c_piix4 ahci mii libahci wmi gpio_amdpt gpio_generic
[ 6380.977266] CPU: 2 PID: 1830 Comm: Xorg Tainted: G        W         4.18.0-16-generic #17-Ubuntu
[ 6380.977267] Hardware name: System manufacturer System Product Name/PRIME B350M-A, BIOS 0806 07/12/2017
[ 6380.977342] RIP: 0010:generic_reg_wait+0xe4/0x160 [amdgpu]
[ 6380.977343] Code: a9 44 8b 45 20 48 8b 4d 18 89 de 44 89 4d d4 8b 55 10 48 c7 c7 10 d4 6f c0 e8 58 c7 da ff 41 83 7c 24 20 01 44 8b 4d d4 74 02 <0f> 0b 48 83 c4 18 44 89 c8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 41 0f 
[ 6380.977377] RSP: 0018:ffffa42742347768 EFLAGS: 00010297
[ 6380.977379] RAX: 0000000000000000 RBX: 000000000000000a RCX: 0000000000000000
[ 6380.977380] RDX: 0000000000000000 RSI: ffff9212ce6964b8 RDI: ffff9212ce6964b8
[ 6380.977381] RBP: ffffa427423477a8 R08: 00000000000ee8b1 R09: 0000000000010200
[ 6380.977383] R10: 0000000000000004 R11: ffffffffbb58880d R12: ffff9212cbc83e80
[ 6380.977384] R13: 0000000000000bb9 R14: 0000000000010000 R15: 0000000000000000
[ 6380.977386] FS:  00007f7534b31a80(0000) GS:ffff9212ce680000(0000) knlGS:0000000000000000
[ 6380.977387] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 6380.977389] CR2: 00007f47c1655000 CR3: 0000000407850000 CR4: 00000000003406e0
[ 6380.977390] Call Trace:
[ 6380.977476]  dce110_stream_encoder_dp_blank+0x12f/0x1a0 [amdgpu]
[ 6380.977553]  dce110_blank_stream+0x57/0x90 [amdgpu]
[ 6380.977627]  core_link_disable_stream+0x57/0x220 [amdgpu]
[ 6380.977703]  dce110_reset_hw_ctx_wrap+0xcd/0x1e0 [amdgpu]
[ 6380.977783]  ? pp_dpm_dispatch_tasks+0x48/0x60 [amdgpu]
[ 6380.977859]  dce110_apply_ctx_to_hw+0x52/0xa30 [amdgpu]
[ 6380.977922]  ? amdgpu_pm_compute_clocks+0x17/0x20 [amdgpu]
[ 6380.977997]  ? pplib_apply_display_requirements+0x1c3/0x1d0 [amdgpu]
[ 6380.978071]  ? dce110_set_bandwidth+0x1d2/0x200 [amdgpu]
[ 6380.978145]  dc_commit_state+0x306/0x5b0 [amdgpu]
[ 6380.978216]  ? dc_stream_get_vblank_counter+0x57/0x60 [amdgpu]
[ 6380.978235]  ? drm_calc_timestamping_constants+0x109/0x150 [drm]
[ 6380.978314]  ? dal_irq_service_set_generic+0x5b/0x70 [amdgpu]
[ 6380.978395]  amdgpu_dm_atomic_commit_tail+0x395/0xe80 [amdgpu]
[ 6380.978401]  ? _cond_resched+0x19/0x30
[ 6380.978403]  ? wait_for_completion_timeout+0x38/0x140
[ 6380.978406]  ? _cond_resched+0x19/0x30
[ 6380.978408]  ? wait_for_completion_interruptible+0x35/0x1a0
[ 6380.978420]  commit_tail+0x42/0x70 [drm_kms_helper]
[ 6380.978430]  drm_atomic_helper_commit+0x113/0x120 [drm_kms_helper]
[ 6380.978514]  amdgpu_dm_atomic_commit+0x8d/0xa0 [amdgpu]
[ 6380.978541]  drm_atomic_commit+0x4a/0x50 [drm]
[ 6380.978567]  drm_atomic_connector_commit_dpms+0xe0/0x100 [drm]
[ 6380.978589]  drm_mode_obj_set_property_ioctl+0x187/0x2b0 [drm]
[ 6380.978608]  ? drm_mode_connector_set_obj_prop+0x90/0x90 [drm]
[ 6380.978626]  drm_mode_connector_property_set_ioctl+0x3b/0x60 [drm]
[ 6380.978642]  drm_ioctl_kernel+0xa4/0xf0 [drm]
[ 6380.978658]  drm_ioctl+0x227/0x400 [drm]
[ 6380.978676]  ? drm_mode_connector_set_obj_prop+0x90/0x90 [drm]
[ 6380.978681]  ? ep_send_events_proc+0x81/0x1b0
[ 6380.978683]  ? ep_modify+0x160/0x160
[ 6380.978742]  amdgpu_drm_ioctl+0x4f/0x90 [amdgpu]
[ 6380.978746]  do_vfs_ioctl+0xa8/0x620
[ 6380.978749]  ? ep_modify+0x71/0x160
[ 6380.978752]  ksys_ioctl+0x67/0x90
[ 6380.978755]  __x64_sys_ioctl+0x1a/0x20
[ 6380.978759]  do_syscall_64+0x5a/0x110
[ 6380.978762]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 6380.978764] RIP: 0033:0x7f7535e683c7
[ 6380.978765] Code: 00 00 90 48 8b 05 c9 3a 0d 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 99 3a 0d 00 f7 d8 64 89 01 48 
[ 6380.978798] RSP: 002b:00007ffc8c6008c8 EFLAGS: 00003246 ORIG_RAX: 0000000000000010
[ 6380.978800] RAX: ffffffffffffffda RBX: 000055cb70c8dd00 RCX: 00007f7535e683c7
[ 6380.978801] RDX: 00007ffc8c600900 RSI: 00000000c01064ab RDI: 000000000000000d
[ 6380.978802] RBP: 00007ffc8c600900 R08: 0000000000000001 R09: 0000000000000000
[ 6380.978804] R10: 0000000000000000 R11: 0000000000003246 R12: 00000000c01064ab
[ 6380.978805] R13: 000000000000000d R14: 000055cb70c8e120 R15: 0000000000000000
[ 6380.978808] ---[ end trace 3753b196b455082c ]---