I have been seeing this error ever since I last updated my system packages. I see the following error message every time during boot:

[   11.504795] [drm:fw_domains_get [i915]] *ERROR* render: timed out waiting for forcewake ack request.
[   11.509800] ------------[ cut here ]------------
[   11.509801] i915 0000:00:02.0: Unclaimed read from register 0x235c
[   11.509850] WARNING: CPU: 4 PID: 494 at drivers/gpu/drm/i915/intel_uncore.c:1182 __unclaimed_reg_debug+0x77/0x90 [i915]
[   11.509851] Modules linked in: bnep joydev mousedev intel_rapl_msr intel_rapl_common x86_pkg_temp_thermal intel_powerclamp kvm_intel iwldvm kvm mac80211 irqbypass snd_hda_codec_hdmi crct10dif_pclmul libarc4 crc32_pclmul snd_hda_codec_conexant ghash_clmulni_intel snd_hda_codec_generic nls_iso8859_1 mei_wdt mei_hdcp iwlwifi aesni_intel nls_cp437 iTCO_wdt btusb snd_hda_intel btrtl crypto_simd vfat btbcm cryptd fat snd_intel_dspcfg btintel glue_helper intel_pmc_bxt wmi_bmof rapl at24 iTCO_vendor_support intel_cstate snd_hda_codec bluetooth snd_hda_core thinkpad_acpi psmouse ecdh_generic snd_hwdep intel_uncore cfg80211 ecc nvram input_leds snd_pcm mei_me pcspkr ledtrig_audio e1000e lpc_ich i2c_i801 tpm_tis tpm_tis_core i2c_smbus snd_timer rfkill mei tpm snd wmi soundcore rng_core evdev battery ac mac_hid usbip_host usbip_core coretemp msr pkcs8_key_parser sg crypto_user ip_tables x_tables ext4 sdhci_pci cqhci serio_raw atkbd sdhci crc32c_generic libps2 crc16 ehci_pci mbcache i8042 jbd2
[   11.509872]  crc32c_intel mmc_core ehci_hcd serio i915 intel_gtt i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops cec rc_core drm agpgart
[   11.509878] CPU: 4 PID: 494 Comm: Xorg Tainted: G        W I       5.8.5-arch1-1 #1
[   11.509878] Hardware name: LENOVO 4236B87/4236B87, BIOS 83ET79WW (1.49 ) 09/05/2016
[   11.509899] RIP: 0010:__unclaimed_reg_debug+0x77/0x90 [i915]
[   11.509900] Code: 48 8b 78 18 4c 8b 77 50 4d 85 f6 74 30 e8 f1 7e 58 ef 45 89 e0 4c 89 e9 4c 89 f2 48 89 c6 48 c7 c7 40 7e 49 c0 e8 8f b1 f5 ee <0f> 0b 83 2d a0 64 21 00 01 5b 5d 41 5c 41 5d 41 5e c3 c3 4c 8b 37
[   11.509901] RSP: 0018:ffffb6198089fd28 EFLAGS: 00010082
[   11.509902] RAX: 0000000000000000 RBX: ffff965446d107e0 RCX: 0000000000000000
[   11.509902] RDX: 0000000000000003 RSI: ffffffffb056ac7f RDI: 00000000ffffffff
[   11.509903] RBP: 0000000000000000 R08: 0000000000000521 R09: 0000000000000004
[   11.509903] R10: 0000000000000000 R11: 0000000000000001 R12: 000000000000235c
[   11.509904] R13: ffffffffc04c00ef R14: ffff96544b06df90 R15: ffff965446d107f8
[   11.509905] FS:  00007fc0db350540(0000) GS:ffff96544e300000(0000) knlGS:0000000000000000
[   11.509906] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   11.509906] CR2: 00007fc0da07d070 CR3: 00000003ef1aa006 CR4: 00000000000606e0
[   11.509907] Call Trace:
[   11.509931]  gen6_read32+0x1da/0x1f0 [i915]
[   11.509952]  i915_reg_read_ioctl+0xc0/0x130 [i915]
[   11.509968]  ? drm_gem_handle_delete+0x73/0x90 [drm]
[   11.509988]  ? intel_uncore_fini_mmio+0xa0/0xa0 [i915]
[   11.509998]  drm_ioctl_kernel+0xb2/0x100 [drm]
[   11.510008]  drm_ioctl+0x208/0x360 [drm]
[   11.510029]  ? intel_uncore_fini_mmio+0xa0/0xa0 [i915]
[   11.510033]  ksys_ioctl+0x82/0xc0
[   11.510035]  __x64_sys_ioctl+0x16/0x20
[   11.510038]  do_syscall_64+0x44/0x70
[   11.510040]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   11.510042] RIP: 0033:0x7fc0dbd08f6b
[   11.510043] Code: 89 d8 49 8d 3c 1c 48 f7 d8 49 39 c4 72 b5 e8 1c ff ff ff 85 c0 78 ba 4c 89 e0 5b 5d 41 5c c3 f3 0f 1e fa b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d d5 ae 0c 00 f7 d8 64 89 01 48
[   11.510044] RSP: 002b:00007ffeffa77968 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[   11.510045] RAX: ffffffffffffffda RBX: 00007ffeffa77a10 RCX: 00007fc0dbd08f6b
[   11.510045] RDX: 00007ffeffa77a10 RSI: 00000000c0106471 RDI: 000000000000000f
[   11.510046] RBP: 00000000c0106471 R08: 0000000000000000 R09: 000055bf48dc6010
[   11.510046] R10: 00007ffeffb17080 R11: 0000000000000246 R12: 0000000000000000
[   11.510047] R13: 000000000000000f R14: 000055bf48e23b00 R15: 0000000000000003
[   11.510049] ---[ end trace cc066b47ea04e946 ]---

The system still kind of works but the rendering performance seems reduced and noticeably sluggish. There are some more

[drm:fw_domains_get [i915]] *ERROR* render: timed out waiting for forcewake ack request.

messages (but without the backtrace) popping up in dmesg. This is on Arch Linux with

- kernel 5.8.5
- mesa 20.1.6
- libdrm 2.4.102