Comment 0 for bug 2044131

There is a regression preventing a user to upgrade from 5.4 kernel to anything that's higher than 5.5. When using such kernel the image orientation is wrong (rotated by 90°C). Also the kernel log contains:
wrz 15 09:19:49 desktop kernel: i915 0000:00:02.0: [drm] Unknown revid 0x06
wrz 15 09:19:49 desktop kernel: rtw_8821ce 0000:01:00.0: Firmware version 24.8.0, H2C version 12
wrz 15 09:19:49 desktop kernel: Console: switching to colour dummy device 80x25
wrz 15 09:19:49 desktop kernel: i915 0000:00:02.0: vgaarb: deactivate vga console
wrz 15 09:19:49 desktop kernel: i915 0000:00:02.0: [drm] couldn't get memory information
wrz 15 09:19:49 desktop kernel: i915 0000:00:02.0: vgaarb: changed VGA decodes: olddecodes=io+mem,decodes=io+mem:o>
wrz 15 09:19:49 desktop kernel: i915 0000:00:02.0: [drm] Finished loading DMC firmware i915/glk_dmc_ver1_04.bin (v>
wrz 15 09:19:49 desktop kernel: ================================================================================
wrz 15 09:19:49 desktop kernel: UBSAN: array-index-out-of-bounds in /build/linux-hwe-5.15-DZkSuT/linux-hwe-5.15-5.>
wrz 15 09:19:49 desktop kernel: index 5 is out of range for type 'u32 [5]'

(full stack trace attached)

The video hardware in use is:
00:02.0 VGA compatible controller [0300]: Intel Corporation UHD Graphics 605 [8086:3185] (rev 06) (prog-if 00 [VGA controller])
(...)
Kernel driver in use: i915
Kernel modules: i915

The user wanted to upgrade from bionic to focal with HWE kernel (they needed it due to some networking hardware they wanted to have supported by the newer kernel).

The user was testing mainline stable kernels and noticed that the last working kernel was the 5.4 series, while anything starting from 5.5 and above is BROKEN (symptoms as described in the first paragraph above).

Together with the user we have run a bisection between v5.4 and v5.5 on the upstream stable kernel and we were able to identify the first broken commit to be:
8f4b1068e7fc3df1a77ac8151767e56b208cc87f drm/i915: Check some transcoder timing minimum limits

To confirm I have reverted this change on top of the HWE kernel for focal and the user have confirmed that this resolved the issue (test build available at ppa:dgadomski/kernel-sf368743).

I am not fully sure what the purpose of this patch was, but I assume the regression was not intended and the hardware should be still supported.

Attaching lshw and lspci output.