Comment 5 for bug 1865130

Just for completeness, some additional info (could be related) - dmesg result:

[ 5.977604] ACPI Error: Method parse/execution failed \_SB.PCI0.PEG0._PRT, AE_NOT_FOUND (20170831/psparse-550)
[ 5.977887] [drm] initializing kernel modesetting (OLAND 0x1002:0x6604 0x17AA:0x380B 0x00).
[ 5.989606] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[ 5.989606] [drm] Driver supports precise vblank timestamp query.
[ 5.995446] vga_switcheroo: enabled
[ 5.995454] i915 0000:00:02.0: vgaarb: changed VGA decodes: olddecodes=io+mem,decodes=io+mem:owns=io+mem
[ 6.003949] ATOM BIOS: Lenovo
[ 6.004078] radeon 0000:01:00.0: VRAM: 2048M 0x0000000000000000 - 0x000000007FFFFFFF (2048M used)
[ 6.004079] radeon 0000:01:00.0: GTT: 2048M 0x0000000080000000 - 0x00000000FFFFFFFF
[ 6.004082] [drm] Detected VRAM RAM=2048M, BAR=128M
[ 6.004082] [drm] RAM width 128bits DDR
[ 6.004128] [TTM] Zone kernel: Available graphics memory: 4041134 kiB
[ 6.004129] [TTM] Zone dma32: Available graphics memory: 2097152 kiB
[ 6.004129] [TTM] Initializing pool allocator
[ 6.004132] [TTM] Initializing DMA pool allocator
[ 6.004147] [drm] radeon: 2048M of VRAM memory ready
[ 6.004148] [drm] radeon: 2048M of GTT memory ready.
[ 6.004156] [drm] Loading oland Microcode
[ 6.004238] [drm] Internal thermal controller without fan control
[ 6.004287] [drm] probing gen 2 caps for device 8086:c01 = 261ad03/e
[ 6.011634] [drm] radeon: dpm initialized
[ 6.013574] [drm] Found VCE firmware/feedback version 50.0.1 / 17!
[ 6.013580] [drm] GART: num cpu pages 524288, num gpu pages 524288
[ 6.014110] ------------[ cut here ]------------
[ 6.014110] Could not determine valid watermarks for inherited state
[ 6.014198] WARNING: CPU: 1 PID: 215 at /build/linux-WUVVsw/linux-4.15.0/drivers/gpu/drm/i915/intel_display.c:14537 intel_modeset_init+0xfcf/0x1010 [i915]
[ 6.014199] Modules linked in: i915(+) radeon(+) ttm i2c_algo_bit drm_kms_helper syscopyarea sysfillrect psmouse sysimgblt fb_sys_fops ahci drm alx libahci mdio video
[ 6.014209] CPU: 1 PID: 215 Comm: systemd-udevd Not tainted 4.15.0-88-generic #88-Ubuntu
[ 6.014210] Hardware name: LENOVO 20238/INVALID, BIOS 79CN46WW(V3.05) 12/23/2013
[ 6.014238] RIP: 0010:intel_modeset_init+0xfcf/0x1010 [i915]
[ 6.014239] RSP: 0018:ffffa52c412bf9b0 EFLAGS: 00010286
[ 6.014240] RAX: 0000000000000000 RBX: ffff92b448fa0000 RCX: ffffffff9f463ae8
[ 6.014241] RDX: 0000000000000001 RSI: 0000000000000096 RDI: 0000000000000247
[ 6.014242] RBP: ffffa52c412bfa40 R08: 00000000000002b1 R09: 0000000000000004
[ 6.014242] R10: 0000000000000040 R11: 0000000000000001 R12: ffff92b455291800
[ 6.014243] R13: ffff92b455425400 R14: 00000000ffffffea R15: ffff92b448fa0358
[ 6.014244] FS: 00007f1ea2076680(0000) GS:ffff92b45f240000(0000) knlGS:0000000000000000
[ 6.014245] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 6.014246] CR2: 0000559644e4ba60 CR3: 000000024964c004 CR4: 00000000001606e0
[ 6.014247] Call Trace:
[ 6.014275] i915_driver_load+0xa73/0xe60 [i915]
[ 6.014299] i915_pci_probe+0x42/0x70 [i915]
[ 6.014303] local_pci_probe+0x47/0xa0
[ 6.014305] pci_device_probe+0x10e/0x1c0
[ 6.014308] driver_probe_device+0x30c/0x490
[ 6.014310] __driver_attach+0xcc/0xf0
[ 6.014311] ? driver_probe_device+0x490/0x490
[ 6.014312] bus_for_each_dev+0x70/0xc0
[ 6.014314] driver_attach+0x1e/0x20
[ 6.014315] bus_add_driver+0x1c7/0x270
[ 6.014316] ? 0xffffffffc072c000
[ 6.014321] driver_register+0x60/0xe0
[ 6.014322] ? 0xffffffffc072c000
[ 6.014323] __pci_register_driver+0x5a/0x60
[ 6.014349] i915_init+0x5c/0x5f [i915]
[ 6.014352] do_one_initcall+0x52/0x19f
[ 6.014355] ? __vunmap+0x8e/0xc0
[ 6.014357] ? _cond_resched+0x19/0x40
[ 6.014360] ? kmem_cache_alloc_trace+0xa6/0x1b0
[ 6.014362] ? do_init_module+0x27/0x213
[ 6.014364] do_init_module+0x5f/0x213
[ 6.014366] load_module+0x16bc/0x1f10
[ 6.014371] ? ima_post_read_file+0x96/0xa0
[ 6.014373] SYSC_finit_module+0xfc/0x120
[ 6.014374] ? SYSC_finit_module+0xfc/0x120
[ 6.014378] SyS_finit_module+0xe/0x10
[ 6.014380] do_syscall_64+0x73/0x130
[ 6.014382] entry_SYSCALL_64_after_hwframe+0x3d/0xa2
[ 6.014383] RIP: 0033:0x7f1ea1b80839
[ 6.014384] RSP: 002b:00007fffced705c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
[ 6.014385] RAX: ffffffffffffffda RBX: 0000559644e3dda0 RCX: 00007f1ea1b80839
[ 6.014386] RDX: 0000000000000000 RSI: 00007f1ea185f145 RDI: 0000000000000012
[ 6.014387] RBP: 00007f1ea185f145 R08: 0000000000000000 R09: 00007fffced706e0
[ 6.014387] R10: 0000000000000012 R11: 0000000000000246 R12: 0000000000000000
[ 6.014388] R13: 0000559644e37ed0 R14: 0000000000020000 R15: 0000559644e3dda0
[ 6.014389] Code: e9 46 fc ff ff 48 c7 c6 d7 ad 6b c0 48 c7 c7 2f a1 6b c0 e8 64 18 a6 dd 0f 0b e9 73 fe ff ff 48 c7 c7 b0 05 6d c0 e8 51 18 a6 dd <0f> 0b e9 4b fe ff ff 48 c7 c6 e4 ad 6b c0 48 c7 c7 2f a1 6b c0
[ 6.014406] ---[ end trace 113e5791d40532e4 ]---
[ 6.014441] [drm] probing gen 2 caps for device 8086:c01 = 261ad03/e
[ 6.014445] [drm] PCIE gen 3 link speeds already enabled
[ 6.022044] [drm] PCIE GART of 2048M enabled (table at 0x00000000001D6000).
[ 6.022159] radeon 0000:01:00.0: WB enabled
[ 6.022161] radeon 0000:01:00.0: fence driver on ring 0 use gpu addr 0x0000000080000c00 and cpu addr 0x (ptrval)
[ 6.022161] radeon 0000:01:00.0: fence driver on ring 1 use gpu addr 0x0000000080000c04 and cpu addr 0x (ptrval)
[ 6.022162] radeon 0000:01:00.0: fence driver on ring 2 use gpu addr 0x0000000080000c08 and cpu addr 0x (ptrval)
[ 6.022163] radeon 0000:01:00.0: fence driver on ring 3 use gpu addr 0x0000000080000c0c and cpu addr 0x (ptrval)
[ 6.022164] radeon 0000:01:00.0: fence driver on ring 4 use gpu addr 0x0000000080000c10 and cpu addr 0x (ptrval)
[ 6.022369] radeon 0000:01:00.0: fence driver on ring 5 use gpu addr 0x0000000000075a18 and cpu addr 0x (ptrval)
[ 6.076085] usb 3-8: new high-speed USB device number 3 using xhci_hcd
[ 6.122959] radeon 0000:01:00.0: failed VCE resume (-110).
[ 6.122963] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[ 6.122964] [drm] Driver supports precise vblank timestamp query.
[ 6.122965] radeon 0000:01:00.0: radeon: MSI limited to 32-bit
[ 6.122999] radeon 0000:01:00.0: radeon: using MSI.
[ 6.123030] [drm] radeon: irq initialized.

The above is while works on linux-firmware=1.173.12. It was that same before last upgrade (to 1.173.15) and after the reverting (which partially solve the issue). Hope the info (reported on many other places) could help figuring out the real problem root. The last firmware update just shows a symptom (the hardest one), I think.