[PATCH 21.02] ipq806x: backport cpufreq changes to 5.4

[Shane Synan]

> -----Original Message-----
> Sent: 6/17/21 1:33 AM
> To: openwrt-devel at lists.openwrt.org
> Cc: Ansuel Smith <ansuelsmth at gmail.com>
> Subject: [PATCH 21.02] ipq806x: backport cpufreq changes to 5.4
> 

In the time since submitting this, I've continued testing this
change on my ZyXEL NBG6817.  I'm reasonably confident this fixes my
issue (11/11 successes), and if there's any further testing that
would help, let me know!

I have tried to recreate this issue with stress-ng.  Unfortunately,
my efforts so far have only discovered new and seemingly-unrelated
ways to cause kernel panics.  Though this patch restores pre-21.02
stability for me, it's clearly not the only issue on ipq806x.

Others on the OFTC/#openwrt-devel IRC channel have kindly informed me
it would have helped to include a version of my test results and
rationale in the commit message itself - feel free to amend when
merging, or if it would be easier, I'm happy to submit a PATCHv2
instead!

In the interim, I'll keep verifying this.  Given the frequency of
crashes without this patch, I won't be able to return to official
21.02 builds meanwhile.

I've also CC'd Baptiste due to this May mailing post:
https://lists.openwrt.org/pipermail/openwrt-devel/2021-May/035153.html
Pardon if this was out of place.


Test case:

OpenSSH configured as secondary SSH server, locked to SFTP and
chroot'd to an external USB HDD.  Deja Dup (duplicity frontend)
runs on my Linux computers, backing up roughly 223 GB compressed and
encrypted in about 7 hours.  This happens in 25 MB chunks, so the
router sees bursts of CPU/memory/IO activity with pauses in between.

See "Environment" below as well.

* WITHOUT this patch, running on 21.02rc1/rc2:

5/30 SFTP transfers succeed, with at most 2 succeeding in a row.

21.02.0rc1: 4/25 backups succeeded
21.02.0rc2: 1/5 backups succeeded

Noted in the bug report here:
https://bugs.openwrt.org/index.php?do=details&task_id=3099#comment9712

I've been investigating this for longer than a month.  If desired, I
can retest with the same "openwrt/openwrt" commit, minus the CPU
patch.

* WITH this patch, built atop 21.02 branch commit
072d0afb8fa6359541568081c23fe2d8d411651c:

11/11 SFTP transfers succeed all consecutively, as noted in the bug
report:
https://bugs.openwrt.org/index.php?do=details&task_id=3099#comment9820

Note: I did not need to apply the DTSI patches for this success.
However, they did not cause any issue, either - my previous time spent
running a May 18th snapshot build went just fine.


Environment:

ZyXEL NBG6817 as router and access point connected to ISP modem:

* 3 local networks (primary, guest, openwireless.org) with
3x(2.4+5 GHz) corresponding WiFi SSIDs

* Additional packages:
nano ncdu luci-ssl openssh-sftp-server mosh-server
luci-app-advanced-reboot luci-app-ddns luci-app-sqm luci-app-openvpn
openvpn-openssl luci-app-nlbwmon stubby hostapd-utils wget-ssl
openssh-server shadow-useradd iperf3

* Additional packages for USB 3 external HDD:
block-mount e2fsprogs kmod-fs-ext4 kmod-usb-storage kmod-usb2
kmod-usb3 kmod-usb-storage-uas

* Dropbear remains the primary SSH daemon.  OpenSSH is configured to
run on a different port, locked down to SFTP access only via chroot
to the USB HDD.

* ASUS RT-AC68U running FreshTomato is connected via Ethernet as a
secondary 3x(2.4+5 GHz) AP, using VLAN tagging

* Other seemingly small configuration tweaks which I can share if it
would help


I recognize that OpenWRT 21.02.0 stable is nearly upon us.  If
there's anything else I can do to help verify this change, let me
know.  Your time is appreciated.


Thanks,
Shane