I have a MacBookPro6,2 that I'm running the mainline 5.15-rc3 ubuntu kernel on successfully. I installed the 5.15-rc5 kernel (the 5.15-rc4 didn't build) and the system wouldn't boot, erroring out with the error below. I also see the same issues using the ubuntu mainline build of 5.15-rc6 and 5.15-rc7.
This is copied from a picture I took of the error screen where the boot halts:
[ 2.554921] RDX: 0000000000000000 RSI: 0000560e0c741670 RDI: 0000000000000015
[ 2.554925] RBP: 0000000000020000 ROB: 0000000000000000 R09: 0000000000000000
[ 2.554928] R10: 0000000000000015 R11: 0000000000000246 R12: 0000560e0c741670
[ 2.554931] R13: 0000560e0c74b980 R14: 0000000000000000 R15: 0000560e0c7362c0
[ 2.554936] Modules linked in: hid_appleir (+) hid_apple i915(+) 12c_algo_bitm hid_generic.drm_kms_helper syscopyarea sysfillrect wl (POE) sysimgblt uas crc e_pclmul fb_sys_fops firewire_ohci usb_storage cec usbhid firewire_core hid crc tu_t rc_core cfg80211 ahci 12c_1801 libahci i2c_smbus tg3 1pc_ich drm apple_gm video apple_bl
[ 2.554967] [ end trace a9fec12cca81a98e ]---
[ 2.554970] RIP: 0010: intel_dp_sync_state+oxeo/oxfo, [1915]
[ 2.555098] Code: 85 69 ff ff ff 48 8b 9f 70 01:00 00 80 bb 83 01 00 00 00 of
85 64 ff ff ff 48 8d bb 70 01 00 00 e8 f5 cb ff ff e9 53 ff ff ff <0f> ob 66 66
2e of if 84 00 00 00 00 00 0f 1f 00 of 1f 44 00 00 55
[ 2.555104] RSP: 0018:ffffae12c06ef898 EFLAGS: 00010282
[ 2.555108] RAX: ffffffffffffffff RBX: ffff99b099034000
ROX: ffff99b097bc03e0
[ 2.555112] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff99b0990341b6
[ 2.555115] RBP: ffffae12c06ef8b8 R08: 00000000ffffff92 R09: ffffffffc0c9cb2c
[ 2.555119] R10: 0000000000000008 R11: ffff99b099034e08 R12: 0000000000000000
[ 2.555122] R13: 0000000000000000 R14: 0000000000000004 R15: ffff99b099034000
[ 2.555125] FS: 00007fd7808a08c0 (0000) GS:ffff99b1c7c80000 (0000) knlGS:00000
00000000000
[ 2.555130] CS: 0010 DS: 0000 ES: 0000 CRO: 0000000080050033
[ 2.555133] CR2: 0000560e0c7395b8 CR3: 0000000100d02000 CR4: 00000000000006e0
[ 2.555244] Console: switching to colour frame buffer device 210x65
