T20 Cpuidle Freeze

[Marcel Ziswiler <marcel.ziswiler@toradex.com>]

Hi Rafael, dear community

One of our customers reported seeing freezes when running the LTS Linux
kernel 4.9.x on our Toradex Colibri T20 modules [1]. I was able to
reproduce a complete SoC lock-up after a few minutes also running the
latest 4.14-rc7 while LTS 4.4.x seemed to run stable.

Having attempted a multi-level bisection points towards the following
first bad commit:

9c4b2867ed7c8c8784dd417ffd16e705e81eb145

cpuidle: menu: Fix menu_select() for CPUIDLE_DRIVER_STATE_START == 0

Unfortunately as drivers/cpuidle/governors/menu.c has gotten further
edits since it seems not trivial to just revert it.

However I found out that it indeed has to do with CPU idle as when I
did disable the CONFIG_CPU_IDLE Linux kernel configuration option also
LTS 4.9.59 as well as latest 4.14-rc7 run now stable overnight.

Does anybody have any clue what exactly may be happening and/or why
cpuidle may not run stable on T20? Or is everybody always just
disabling cpuidle on T20 anyway?

Thanks!

[1] https://www.toradex.com/community/questions/16838/actual-lts-kernel
-49-on-colibri-t20.html

Best regards - Mit freundlichen Grüssen - Meilleures salutations

Marcel Ziswiler
Platform Manager Embedded Linux

Toradex AG
Altsagenstrasse 5 | 6048 Horw/Luzern | Switzerland | T: +41 41 500 48 00
(main line) | Direct: +41 41 500 48 10