[PATCH 21.02] ipq806x: backport cpufreq changes to 5.4

[Shane Synan]

On 6/28/21 2:10 AM, Shane Synan wrote:
> On 6/27/21 6:10 PM, Ansuel Smith wrote:
>> It's good but consider that also the dts changes are required and also there
>> is a pending pr that has to be merged or ipq8065 device will run at lower speed.
>> The new cpufreq have changed the node definition
>> This is the pr I'm talking about.
>> https://github.com/openwrt/openwrt/pull/4192
>>
>> So in short this backport lacks the dts changes and the pr4192 is mandatory or
>> we will introduce perf regression in 21
>>
> 
> Thank you for pointing out the details of the DTS changes and CPU
> performance.  Originally I was trying to achieve the smallest
> backport, but in hindsight, it makes far more sense to avoid
> frankensteining with partial changes.  I appreciate your patience and
> advice!
> 
> Meanwhile, until PR #4192 can be reviewed/merged to master (so there's
> commits to actually backport), I've thrown together a rough draft of
> what changes would need backported:

Now that https://github.com/openwrt/openwrt/pull/4192 is merged,
including four successful tests on Linux kernel v5.4, I've tried
backporting all the CPU frequency/DTS/etc changes that appeared
relevant, as shown here:
https://github.com/openwrt/openwrt/compare/openwrt-21.02...digitalcircuit:openwrt-21.02-cpufreq-dtsivolt-cache
(some commits were modified to drop kernel v5.10 patches)

Unfortunately, my initial attempt is unstable again.  I've gotten
3 reboots so far within a few hours of SFTP testing.  Unlike before,
nothing displays on the router's soldered-on serial console headers.

Given these commits work just fine on the "master" branch, and on
"21.02" it worked to change the CPU governor *without* the DTSI
backports and cache (i.e. only the first commit), I strongly suspect I
goofed up and missed backporting something important.

Ansuel, do you have any suggestions on what else I should look for or
try tinkering with?

Meanwhile, just to see what happens in an attempt to narrow things
down, I'm testing a build without the DTSI backports (all commits linked
above except for "ipq806x: refresh dtsi patches" and "ipq806x: apply
correct voltage tolerance").  So far, it boots, though I haven't run a
full test.  Regardless, it's not a proper solution, just a
troubleshooting attempt.