My problems with HDMI started several months back. At first this just amounted to long wait times for external monitors to connect. Then it progressed to unstable connections and extremely long connect and disconnect times, often lasting several minutes, during which time my desktop would freeze. Recently, after I switched from Xfce to LXDE, the problems apparently stopped, or so I hoped. Alas, a couple of nights ago, inevitably, my HDMI interface stopped working altogether.

I eliminated a possible problem with the monitor and/or cables, by testing several monitors and cables. I also found the same problem when I booted up in the two previous kernels, and in the Xfce, Gnome and lubuntu environments. ( I am currently using 4.17.12-200.fc28.x86_64)

Curiously, when I run the Monitor/Display tool in any of the above desktops it not only correctly detects monitors that are connected to the HDMI interface, it also apparently "connects" to them, though, in reality no actual signal is transmitted to the displays. I also ran xrandr and arandr, which also detect the monitors correctly, but are also unable to make actual connections.

I have no idea whether my HDMI is physically broken, which would probably mean replacing the motherboard, or if this is a Linux graphics controller issue, though I suspect and need to eliminate the latter. Admittedly, at 10, my machine is rather old, but I am very fond of it, and it otherwise functions very well. It has an Intel GM965/GL960 Integrated Graphics Controller, lspci yields:

$ lspci -vnn | grep VGA -A 12
00:02.0 VGA compatible controller [0300]: Intel Corporation Mobile GM965/GL960 Integrated Graphics Controller (primary) [8086:2a02] (rev 0c) (prog-if 00 [VGA controller])
Subsystem: Dell Inspiron 1525 [1028:022f]
Flags: bus master, fast devsel, latency 0, IRQ 16
Memory at fea00000 (64-bit, non-prefetchable) [size=1M]
Memory at e0000000 (64-bit, prefetchable) [size=256M]
I/O ports at eff8 [size=8]
[virtual] Expansion ROM at 000c0000 [disabled] [size=128K]
Capabilities: <access denied>
Kernel driver in use: i915
Kernel modules: i915

00:02.1 Display controller [0380]: Intel Corporation Mobile GM965/GL960 Integrated Graphics Controller (secondary) [8086:2a03] (rev 0c)
Subsystem: Dell Inspiron 1525 [1028:022f]

The last time I checked it was the case that the Linux graphics driver was actually written by Intel, which I think is still true. The system log produces the following messages each time I attempt to connect via HDMI to a monitor (most recent first):

01:18:18 kernel: [drm:drm_atomic_helper_wait_for_dependencies [drm_kms_helper]] *ERROR* [CONNECTOR:56:SVIDEO-1] flip_done timed out
01:17:58 kernel: ---[ end trace 629e0d07d0f29f55 ]---
01:17:58 kernel: Code: cb ca 0f 0b e9 2d ff ff ff 48 89 e6 4c 89 f7 e8 01 83 d0 ca 45 85 e4 0f 85 0f ff ff ff 89 ee 48 c7 c7 40 b3 40 c0 e8 d4 fc cb ca <0f> 0b e9 fa fe ff ff e8 5e fa cb ca 0f 1f 40 00 66 2e 0f 1f 84
01:17:58 kernel: R13: 000000000000000c R14: 000000000000000c R15: 00007ffd9079be80
01:17:58 kernel: R10: 00000000000002d0 R11: 0000000000000246 R12: 00000000c05064a7
01:17:58 kernel: RBP: 00007ffd9079be80 R08: 00000000035d9c60 R09: 0000000000000007
01:17:58 kernel: RDX: 00007ffd9079be80 RSI: 00000000c05064a7 RDI: 000000000000000c
01:17:58 kernel: RAX: ffffffffffffffda RBX: 0000000002a31c30 RCX: 00007fa28f420ec7
01:17:58 kernel: RSP: 002b:00007ffd9079be48 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
01:17:58 kernel: RIP: 0033:0x7fa28f420ec7
01:17:58 kernel: entry_SYSCALL_64_after_hwframe+0x44/0xa9
01:17:58 kernel: Call Trace:
01:17:58 kernel: CR2: 00007f8e3317d668 CR3: 00000000b69e6000 CR4: 00000000000006e0
01:17:58 kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
01:17:58 kernel: FS: 00007fa292199ac0(0000) GS:ffff8826dfd00000(0000) knlGS:0000000000000000
01:17:58 kernel: R13: 0000000021000012 R14: ffff8826d63be168 R15: ffff8825c7a3fc00
01:17:58 kernel: R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
01:17:58 kernel: RBP: 0000000000000001 R08: 0000000000000030 R09: 000000000000071e
01:17:58 kernel: RDX: 0000000000000007 RSI: 0000000000000086 RDI: ffff8826dfd16930
01:17:58 kernel: RAX: 0000000000000000 RBX: ffff8826d4ec8000 RCX: 0000000000000006
01:17:58 kernel: RSP: 0018:ffffb5bb00a3f9f0 EFLAGS: 00010286
01:17:58 kernel: RIP: 0010:drm_wait_one_vblank+0x166/0x180 [drm]
01:17:58 kernel: Hardware name: Dell Inc. Inspiron 1525 /0WP007, BIOS A08 01/07/2008
01:17:58 kernel: CPU: 1 PID: 2488 Comm: Xorg Tainted: G W OE 4.17.12-200.fc28.x86_64 #1
01:17:58 kernel: dell_smbios dcdbas dell_wmi_descriptor snd_hda_codec_idt arc4 snd_hda_codec_generic iwl3945 snd_hda_codec_hdmi coretemp dell_smm_hwmon snd_hda_intel snd_hda_codec iwlegacy snd_hda_core mac80211 joydev snd_hwdep snd_seq i2c_i801 cfg80211 rfkill snd_seq_device snd_pcm lpc_ich r592 memstick snd_timer snd soundcore shpchp wmi pcc_cpufreq acpi_cpufreq vboxpci(OE) vboxnetadp(OE) vboxnetflt(OE) vboxdrv(OE) dm_crypt i915 sdhci_pci cqhci sdhci mmc_core firewire_ohci serio_raw firewire_core ata_generic pata_acpi crc_itu_t sky2 i2c_algo_bit drm_kms_helper drm video ecryptfs
01:17:58 kernel: Modules linked in: rfcomm fuse xt_CHECKSUM ipt_MASQUERADE nf_nat_masquerade_ipv4 tun nf_conntrack_netbios_ns nf_conntrack_broadcast xt_CT ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 xt_conntrack ccm devlink ip_set nfnetlink ebtable_nat ebtable_broute bridge stp llc ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack libcrc32c iptable_mangle iptable_raw iptable_security ebtable_filter ebtables ip6table_filter ip6_tables bnep binfmt_misc sunrpc uvcvideo videobuf2_vmalloc videobuf2_memops videobuf2_v4l2 videobuf2_common videodev media btusb btrtl btbcm btintel bluetooth ecdh_generic iTCO_wdt gpio_ich iTCO_vendor_support dell_wmi sparse_keymap dell_laptop wmi_bmof
01:17:58 kernel: WARNING: CPU: 1 PID: 2488 at drivers/gpu/drm/drm_vblank.c:1084 drm_wait_one_vblank+0x166/0x180 [drm]
01:17:58 kernel: vblank wait timed out on crtc 1
01:17:58 kernel: ------------[ cut here ]------------

For the most part I have no idea what any of that means . However, I have of course rooted around on the web for any evidence of people suffering similar problems. Most significantly, I learned that the error in the first line has appeared in various places over the last few years and, as I understand it, is probably related to an "old" Intel bug in the Linux kernel:

Red Hat Bugzilla Bug 1534300
https://bugzilla.redhat.com/show_bug.cgi?id=1534300

which primarily causes slow boot times, (which I am also affected by). However, I am not sure that this bug is causing my HDMI problem, or if it is just a coincidence. Either way, it doesn't look as though anyone at intel is going to fix it. Also, I am concerned that if this bug is responsible, it could lead to further problems down the line.

Apologies for the long post. I would be eternally grateful for any constructive advice on how to proceed.

Thanks!