Created attachment 144154
Test file: read-dpcd.c

While working with the Ubuntu maintainers of fwupd, they've determined that I have an issue with the AMD driver on Ubuntu's 5.0 kernel in 19.04. In the sample program that they provided (see read-dpcd.c attached) the call to aux_read(fd, REG_RC_CAP, buf, 1) hangs on my machine. They recommended I post the issue here.

Machine is a Dell 7730 with AMD WX4150 graphics.

See the original bug report here:
https://bugs.launchpad.net/ubuntu/+source/fwupd/+bug/1826691


Not sure if it's related, but here are dmesg warnings from the other ticket.

Apr 23 19:29:14 texas kernel: [ 133.673290] [drm] REG_WAIT timeout 10us * 160 tries - submit_channel_request line:246
Apr 23 19:29:14 texas kernel: [ 133.673348] WARNING: CPU: 6 PID: 2467 at drivers/gpu/drm/amd/amdgpu/../display/dc/dc_helper.c:249 generic_reg_wait.cold.3+0x25/0x2c [amdgpu]
Apr 23 19:29:14 texas kernel: [ 133.673349] Modules linked in: thunderbolt rfcomm xt_owner ip6table_filter ip6_tables ipt_MASQUERADE iptable_nat nf_nat_ipv4 nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 libcrc32c bridge xt_CHECKSUM xt_tcpudp stp llc iptable_filter iptable_mangle bpfilter ccm snd_hda_codec_realtek snd_hda_codec_generic pci_stub vboxpci(OE) vboxnetadp(OE) vboxnetflt(OE) cmac vboxdrv(OE) bnep binfmt_misc dell_rbtn nls_iso8859_1 joydev arc4 snd_soc_skl snd_soc_hdac_hda snd_hda_ext_core snd_soc_skl_ipc snd_soc_sst_ipc snd_soc_sst_dsp snd_soc_acpi_intel_match snd_soc_acpi snd_soc_core snd_compress ac97_bus intel_rapl snd_pcm_dmaengine x86_pkg_temp_thermal intel_powerclamp coretemp snd_hda_codec_hdmi kvm_intel snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep crct10dif_pclmul i915 snd_pcm crc32_pclmul iwlmvm uvcvideo amdgpu snd_seq_midi ghash_clmulni_intel snd_seq_midi_event mac80211 videobuf2_vmalloc kvmgt videobuf2_memops vfio_mdev videobuf2_v4l2 snd_rawmidi dell_laptop mdev videobuf2_common
Apr 23 19:29:14 texas kernel: [ 133.673362] ledtrig_audio vfio_iommu_type1 videodev dell_smm_hwmon vfio snd_seq dell_wmi media kvm chash btusb snd_seq_device amd_iommu_v2 btrtl snd_timer btbcm dell_smbios gpu_sched irqbypass btintel dcdbas ttm aesni_intel iwlwifi bluetooth drm_kms_helper aes_x86_64 crypto_simd cryptd glue_helper rtsx_pci_ms input_leds snd drm ecdh_generic intel_cstate mei_me ucsi_acpi cfg80211 serio_raw dell_wmi_descriptor intel_wmi_thunderbolt wmi_bmof memstick i2c_algo_bit mei fb_sys_fops intel_rapl_perf idma64 syscopyarea hid_multitouch processor_thermal_device soundcore sysfillrect virt_dma typec_ucsi sysimgblt intel_soc_dts_iosf intel_pch_thermal typec int3403_thermal int340x_thermal_zone dell_smo8800 acpi_pad intel_hid int3400_thermal mac_hid acpi_thermal_rel sparse_keymap sch_fq_codel parport_pc ppdev lp parport ip_tables x_tables autofs4 hid_generic rtsx_pci_sdmmc nvme e1000e i2c_i801 intel_lpss_pci rtsx_pci nvme_core intel_lpss i2c_hid wmi hid video pinctrl_cannonlake pinctrl_intel
Apr 23 19:29:14 texas kernel: [ 133.673381] CPU: 6 PID: 2467 Comm: fwupd Tainted: G OE 5.0.0-13-generic #14-Ubuntu
Apr 23 19:29:14 texas kernel: [ 133.673382] Hardware name: Dell Inc. Precision 7730/05W5TJ, BIOS 1.7.0 02/19/2019
Apr 23 19:29:14 texas kernel: [ 133.673417] RIP: 0010:generic_reg_wait.cold.3+0x25/0x2c [amdgpu]
Apr 23 19:29:14 texas kernel: [ 133.673418] Code: e9 37 7e fe ff 44 8b 45 20 48 8b 4d 18 48 c7 c7 40 34 17 c1 8b 55 10 8b 75 d4 e8 3b ce 82 e1 41 83 7d 20 01 0f 84 0c c3 fe ff <0f> 0b e9 05 c3 fe ff 55 48 89 e5 e8 5d de ec ff 48 c7 c7 00 a0 18
Apr 23 19:29:14 texas kernel: [ 133.673419] RSP: 0018:ffffbbaa0612fbb0 EFLAGS: 00010297
Apr 23 19:29:14 texas kernel: [ 133.673420] RAX: 0000000000000049 RBX: 00000000000000a1 RCX: 0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.673420] RDX: 0000000000000000 RSI: ffff94843c196448 RDI: ffff94843c196448
Apr 23 19:29:14 texas kernel: [ 133.673420] RBP: ffffbbaa0612fbf8 R08: 0000000000000001 R09: 00000000000004fa
Apr 23 19:29:14 texas kernel: [ 133.673421] R10: 0000000000000004 R11: 0000000000000000 R12: 0000000000005c04
Apr 23 19:29:14 texas kernel: [ 133.673421] R13: ffff948431de5840 R14: 00000000ffffffff R15: ffff948431de5840
Apr 23 19:29:14 texas kernel: [ 133.673422] FS: 00007ff849b11b40(0000) GS:ffff94843c180000(0000) knlGS:0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.673422] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
Apr 23 19:29:14 texas kernel: [ 133.673423] CR2: 00007ff83400f6d8 CR3: 0000000847680006 CR4: 00000000003606e0
Apr 23 19:29:14 texas kernel: [ 133.673423] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.673424] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Apr 23 19:29:14 texas kernel: [ 133.673424] Call Trace:
Apr 23 19:29:14 texas kernel: [ 133.673461] submit_channel_request+0x3fd/0x780 [amdgpu]
Apr 23 19:29:14 texas kernel: [ 133.673492] dc_link_aux_transfer+0xc6/0x150 [amdgpu]
Apr 23 19:29:14 texas kernel: [ 133.673526] dm_dp_aux_transfer+0x61/0x130 [amdgpu]
Apr 23 19:29:14 texas kernel: [ 133.673531] drm_dp_dpcd_access+0x75/0x110 [drm_kms_helper]
Apr 23 19:29:14 texas kernel: [ 133.673533] drm_dp_dpcd_read+0x33/0xc0 [drm_kms_helper]
Apr 23 19:29:14 texas kernel: [ 133.673537] auxdev_read_iter+0xe6/0x1a0 [drm_kms_helper]
Apr 23 19:29:14 texas kernel: [ 133.673539] new_sync_read+0x109/0x170
Apr 23 19:29:14 texas kernel: [ 133.673541] __vfs_read+0x29/0x40
Apr 23 19:29:14 texas kernel: [ 133.673542] vfs_read+0x99/0x160
Apr 23 19:29:14 texas kernel: [ 133.673542] ksys_read+0x55/0xc0
Apr 23 19:29:14 texas kernel: [ 133.673543] __x64_sys_read+0x1a/0x20
Apr 23 19:29:14 texas kernel: [ 133.673545] do_syscall_64+0x5a/0x110
Apr 23 19:29:14 texas kernel: [ 133.673546] entry_SYSCALL_64_after_hwframe+0x44/0xa9
Apr 23 19:29:14 texas kernel: [ 133.673547] RIP: 0033:0x7ff84ccb4d94
Apr 23 19:29:14 texas kernel: [ 133.673548] Code: 84 00 00 00 00 00 41 54 49 89 d4 55 48 89 f5 53 89 fb 48 83 ec 10 e8 5b fc ff ff 4c 89 e2 48 89 ee 89 df 41 89 c0 31 c0 0f 05 <48> 3d 00 f0 ff ff 77 38 44 89 c7 48 89 44 24 08 e8 97 fc ff ff 48
Apr 23 19:29:14 texas kernel: [ 133.673548] RSP: 002b:00007ffe268d7130 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.673549] RAX: ffffffffffffffda RBX: 0000000000000013 RCX: 00007ff84ccb4d94
Apr 23 19:29:14 texas kernel: [ 133.673549] RDX: 0000000000000001 RSI: 00007ffe268d7194 RDI: 0000000000000013
Apr 23 19:29:14 texas kernel: [ 133.673550] RBP: 00007ffe268d7194 R08: 0000000000000000 R09: 00007ff84cca13d0
Apr 23 19:29:14 texas kernel: [ 133.673550] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
Apr 23 19:29:14 texas kernel: [ 133.673550] R13: 00007ffe268d7200 R14: 0000000000000001 R15: 000056469f7bd0e0
Apr 23 19:29:14 texas kernel: [ 133.673552] ---[ end trace b363bbe01edada49 ]---
Apr 23 19:29:14 texas kernel: [ 133.673574] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
Apr 23 19:29:14 texas kernel: [ 133.673576] #PF error: [normal kernel read fault]
Apr 23 19:29:14 texas kernel: [ 133.673577] PGD 0 P4D 0
Apr 23 19:29:14 texas kernel: [ 133.673578] Oops: 0000 [#1] SMP PTI
Apr 23 19:29:14 texas kernel: [ 133.673579] CPU: 6 PID: 2467 Comm: fwupd Tainted: G W OE 5.0.0-13-generic #14-Ubuntu
Apr 23 19:29:14 texas kernel: [ 133.673580] Hardware name: Dell Inc. Precision 7730/05W5TJ, BIOS 1.7.0 02/19/2019
Apr 23 19:29:14 texas kernel: [ 133.673614] RIP: 0010:dal_ddc_close+0xd/0x30 [amdgpu]
Apr 23 19:29:14 texas kernel: [ 133.673615] Code: e8 38 f5 ff ff 48 8b 55 f8 65 48 33 14 25 28 00 00 00 75 02 c9 c3 e8 02 01 84 e1 66 90 0f 1f 44 00 00 55 48 89 e5 53 48 89 fb <48> 8b 7f 08 e8 0a f6 ff ff 48 8b 3b e8 02 f6 ff ff 5b 5d c3 66 2e
Apr 23 19:29:14 texas kernel: [ 133.673615] RSP: 0018:ffffbbaa0612fc28 EFLAGS: 00010246
Apr 23 19:29:14 texas kernel: [ 133.673616] RAX: ffffffffc1052ad0 RBX: 0000000000000000 RCX: 0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.673617] RDX: 00000000ffffffff RSI: 0000000000005c04 RDI: 0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.673617] RBP: ffffbbaa0612fc30 R08: 0000000000000001 R09: 000000000000000a
Apr 23 19:29:14 texas kernel: [ 133.673618] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.673618] R13: ffffbbaa0612fdc0 R14: 0000000000000000 R15: 0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.673619] FS: 00007ff849b11b40(0000) GS:ffff94843c180000(0000) knlGS:0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.673620] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
Apr 23 19:29:14 texas kernel: [ 133.673620] CR2: 0000000000000008 CR3: 0000000847680006 CR4: 00000000003606e0
Apr 23 19:29:14 texas kernel: [ 133.673621] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.673622] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Apr 23 19:29:14 texas kernel: [ 133.673622] Call Trace:
Apr 23 19:29:14 texas kernel: [ 133.673657] release_engine+0x1e/0xd0 [amdgpu]
Apr 23 19:29:14 texas kernel: [ 133.673687] dc_link_aux_transfer+0xfc/0x150 [amdgpu]
Apr 23 19:29:14 texas kernel: [ 133.673720] dm_dp_aux_transfer+0x61/0x130 [amdgpu]
Apr 23 19:29:14 texas kernel: [ 133.673723] drm_dp_dpcd_access+0x75/0x110 [drm_kms_helper]
Apr 23 19:29:14 texas kernel: [ 133.673726] drm_dp_dpcd_read+0x33/0xc0 [drm_kms_helper]
Apr 23 19:29:14 texas kernel: [ 133.673730] auxdev_read_iter+0xe6/0x1a0 [drm_kms_helper]
Apr 23 19:29:14 texas kernel: [ 133.673731] new_sync_read+0x109/0x170
Apr 23 19:29:14 texas kernel: [ 133.673733] __vfs_read+0x29/0x40
Apr 23 19:29:14 texas kernel: [ 133.673734] vfs_read+0x99/0x160
Apr 23 19:29:14 texas kernel: [ 133.673735] ksys_read+0x55/0xc0
Apr 23 19:29:14 texas kernel: [ 133.673736] __x64_sys_read+0x1a/0x20
Apr 23 19:29:14 texas kernel: [ 133.673737] do_syscall_64+0x5a/0x110
Apr 23 19:29:14 texas kernel: [ 133.673738] entry_SYSCALL_64_after_hwframe+0x44/0xa9
Apr 23 19:29:14 texas kernel: [ 133.673739] RIP: 0033:0x7ff84ccb4d94
Apr 23 19:29:14 texas kernel: [ 133.673740] Code: 84 00 00 00 00 00 41 54 49 89 d4 55 48 89 f5 53 89 fb 48 83 ec 10 e8 5b fc ff ff 4c 89 e2 48 89 ee 89 df 41 89 c0 31 c0 0f 05 <48> 3d 00 f0 ff ff 77 38 44 89 c7 48 89 44 24 08 e8 97 fc ff ff 48
Apr 23 19:29:14 texas kernel: [ 133.673740] RSP: 002b:00007ffe268d7130 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.673741] RAX: ffffffffffffffda RBX: 0000000000000013 RCX: 00007ff84ccb4d94
Apr 23 19:29:14 texas kernel: [ 133.673742] RDX: 0000000000000001 RSI: 00007ffe268d7194 RDI: 0000000000000013
Apr 23 19:29:14 texas kernel: [ 133.673742] RBP: 00007ffe268d7194 R08: 0000000000000000 R09: 00007ff84cca13d0
Apr 23 19:29:14 texas kernel: [ 133.673743] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
Apr 23 19:29:14 texas kernel: [ 133.673743] R13: 00007ffe268d7200 R14: 0000000000000001 R15: 000056469f7bd0e0
Apr 23 19:29:14 texas kernel: [ 133.673744] Modules linked in: thunderbolt rfcomm xt_owner ip6table_filter ip6_tables ipt_MASQUERADE iptable_nat nf_nat_ipv4 nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 libcrc32c bridge xt_CHECKSUM xt_tcpudp stp llc iptable_filter iptable_mangle bpfilter ccm snd_hda_codec_realtek snd_hda_codec_generic pci_stub vboxpci(OE) vboxnetadp(OE) vboxnetflt(OE) cmac vboxdrv(OE) bnep binfmt_misc dell_rbtn nls_iso8859_1 joydev arc4 snd_soc_skl snd_soc_hdac_hda snd_hda_ext_core snd_soc_skl_ipc snd_soc_sst_ipc snd_soc_sst_dsp snd_soc_acpi_intel_match snd_soc_acpi snd_soc_core snd_compress ac97_bus intel_rapl snd_pcm_dmaengine x86_pkg_temp_thermal intel_powerclamp coretemp snd_hda_codec_hdmi kvm_intel snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep crct10dif_pclmul i915 snd_pcm crc32_pclmul iwlmvm uvcvideo amdgpu snd_seq_midi ghash_clmulni_intel snd_seq_midi_event mac80211 videobuf2_vmalloc kvmgt videobuf2_memops vfio_mdev videobuf2_v4l2 snd_rawmidi dell_laptop mdev videobuf2_common
Apr 23 19:29:14 texas kernel: [ 133.673754] ledtrig_audio vfio_iommu_type1 videodev dell_smm_hwmon vfio snd_seq dell_wmi media kvm chash btusb snd_seq_device amd_iommu_v2 btrtl snd_timer btbcm dell_smbios gpu_sched irqbypass btintel dcdbas ttm aesni_intel iwlwifi bluetooth drm_kms_helper aes_x86_64 crypto_simd cryptd glue_helper rtsx_pci_ms input_leds snd drm ecdh_generic intel_cstate mei_me ucsi_acpi cfg80211 serio_raw dell_wmi_descriptor intel_wmi_thunderbolt wmi_bmof memstick i2c_algo_bit mei fb_sys_fops intel_rapl_perf idma64 syscopyarea hid_multitouch processor_thermal_device soundcore sysfillrect virt_dma typec_ucsi sysimgblt intel_soc_dts_iosf intel_pch_thermal typec int3403_thermal int340x_thermal_zone dell_smo8800 acpi_pad intel_hid int3400_thermal mac_hid acpi_thermal_rel sparse_keymap sch_fq_codel parport_pc ppdev lp parport ip_tables x_tables autofs4 hid_generic rtsx_pci_sdmmc nvme e1000e i2c_i801 intel_lpss_pci rtsx_pci nvme_core intel_lpss i2c_hid wmi hid video pinctrl_cannonlake pinctrl_intel
Apr 23 19:29:14 texas kernel: [ 133.673765] CR2: 0000000000000008
Apr 23 19:29:14 texas kernel: [ 133.673766] ---[ end trace b363bbe01edada4a ]---
Apr 23 19:29:14 texas kernel: [ 133.696801] RIP: 0010:dal_ddc_close+0xd/0x30 [amdgpu]
Apr 23 19:29:14 texas kernel: [ 133.696804] Code: e8 38 f5 ff ff 48 8b 55 f8 65 48 33 14 25 28 00 00 00 75 02 c9 c3 e8 02 01 84 e1 66 90 0f 1f 44 00 00 55 48 89 e5 53 48 89 fb <48> 8b 7f 08 e8 0a f6 ff ff 48 8b 3b e8 02 f6 ff ff 5b 5d c3 66 2e
Apr 23 19:29:14 texas kernel: [ 133.696805] RSP: 0018:ffffbbaa0612fc28 EFLAGS: 00010246
Apr 23 19:29:14 texas kernel: [ 133.696806] RAX: ffffffffc1052ad0 RBX: 0000000000000000 RCX: 0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.696807] RDX: 00000000ffffffff RSI: 0000000000005c04 RDI: 0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.696808] RBP: ffffbbaa0612fc30 R08: 0000000000000001 R09: 000000000000000a
Apr 23 19:29:14 texas kernel: [ 133.696809] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.696809] R13: ffffbbaa0612fdc0 R14: 0000000000000000 R15: 0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.696810] FS: 00007ff849b11b40(0000) GS:ffff94843c180000(0000) knlGS:0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.696811] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
Apr 23 19:29:14 texas kernel: [ 133.696812] CR2: 0000000000000008 CR3: 0000000847680006 CR4: 00000000003606e0
Apr 23 19:29:14 texas kernel: [ 133.696813] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
Apr 23 19:29:14 texas kernel: [ 133.696813] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400