** Changed in: linux
Status: Unknown => Fix Released
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https://bugs.launchpad.net/bugs/2044131
Title:
i915 regression introduced with 5.5 kernel
Status in Linux:
Fix Released
Status in linux package in Ubuntu:
New
Status in linux source package in Focal:
New
Status in linux source package in Jammy:
New
Status in linux source package in Mantic:
New
Status in linux source package in Noble:
New
Bug description:
[ Impact ]
Commit 8f4b1068e7fc3df1a77ac8151767e56b208cc87f introduced some timing checks
which have been proven invalid for at least some hardware setups. A user trying
to run Focal with HWE 5.15 kernel is not able to get any video output.
After going through bisection between 5.4 and 5.5 this commit was identified.
Reverting it on top of Focal HWE kernel fixes the issue.
The issue has been addressed upstream in DRM tree
(20c2dbff342aec13bf93c2f6c951da198916a455) and has been merge into
linux-next (e0ef2daa8ca8ce4dbc2fd0959e383b753a87fd7d).
dmesg and lspci from the affected configuration are attached to this
bug.
[ Test Plan ]
1. Boot the affected hardware with Ubuntu desktop running kernel v5.5 or
higher.
2. Wait until boot finishes and see the blank screen.
Actual result: there is no video output visible.
Expected result: normal boot process should be visible (e.g. splash), then
GUI should appear.
[ Where problem could occur ]
This bug was a result of assumptions in the checks that turned out to be not
valid for some hardware. The checks were removed from global intel_mode_valid
function and moved into connector specific .mode_valid() hooks, entirely
skiping BXT/GLK DSI connectors.
This should keep the checks where appropriate and skip for hardware
that does not comply to them.
[ Other info ]
Original bug description:
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.
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