Discussion:
ipq40xx cpu frequency
(too old to reply)
Roman Yeryomin
2018-05-04 14:12:16 UTC
Permalink
Hi Christian,

I'm seeing this

[ 1.275858] cpufreq: cpufreq_online: CPU0: Running at unlisted freq:
632000 KHz
[ 1.276620] cpufreq: cpufreq_online: CPU0: Unlisted initial frequency
changed to: 716000 KHz

on ap-dk01 board (I suspect others may be affected too, I don't have hw
to test).

Looks like related to your commit
a44d435c1d ipq40xx: fix apss cpu overclocking spam

While it fixes the original problem described, it would be nice not to
misconfigure the clock anyway.
Also, since the official highest frequency is 716.8MHz, wouldn't it be
more logical to fix it in appropriate board dts (if needed) and not in
the common dtsi?


Regards,
Roman
Christian Lamparter
2018-05-05 18:39:10 UTC
Permalink
Hello,
Post by Roman Yeryomin
I'm seeing this
632000 KHz
[ 1.276620] cpufreq: cpufreq_online: CPU0: Unlisted initial frequency
changed to: 716000 KHz
Sorry, but I'm having this "déjà vu"? I do remember *trying* to talk with
you about this in this thread "ipq806x: add ap.dk01.1 board support" already.
<https://patchwork.ozlabs.org/patch/826312/>
Back then you initially went with 710 MHz and I warned:
|There's a reason to stick with the 666MHz rate though. You should check
|if the device produces messages like:
|[ 1.399981] cpufreq: cpufreq_online: CPU0: Running at unlisted freq: 666000 KHz
|[ 1.400256] cpufreq: cpufreq_online: CPU0: Unlisted initial frequency changed to: 710000 KHz
|(From what I know, the SBL actually sets it to 666MHz)
|
|But there's more. If you look at qualcomm's page, it's says that the
|CPU Clock Speed is 717 MHz: <https://www.qualcomm.com/products/ipq4028>
|
|Since you are working for a OEM/ODM. You could please ask what is the
|right MHz table for these devices? Unfortunately, Qualcomm never got
|around to fix this upstream and without an official statement from them
|it's very difficult to push stuff like this upstream.
Have we come full circle now?
Post by Roman Yeryomin
on ap-dk01 board (I suspect others may be affected too, I don't
have hw to test).
Yes that is true some boards print the same warning (with different
unlisted frequencies). The patch was sent upstream to linux-clk along
with a request on how this should be handled. Sadly no maintainer
has replied, even though the some of the IPQ40XX boards are crashing
without it.
Post by Roman Yeryomin
Looks like related to your commit
a44d435c1d ipq40xx: fix apss cpu overclocking spam
While it fixes the original problem described, it would be nice not to
misconfigure the clock anyway.
Hmm? I think this is a misunderstanding, or are you jumping to conclusions?
The patch does not misconfigure the clock. The 900-clk-fix.patch
message explains in detail what the patch does and why:
|This patch attempts to fix the issue by modifying
|clk_cpu_div_round_rate(), clk_cpu_div_set_rate(), clk_cpu_div_recalc_rate()
|to use a new qcom_find_freq_close() function, which returns the closest
|matching frequency, instead of the next higher. This way, the SoC in
|the FB4040 (with its max clock speed of 710.4 MHz) will no longer
|try to overclock to 761 MHz.
Post by Roman Yeryomin
Also, since the official highest frequency is 716.8MHz, wouldn't it be
more logical to fix it in appropriate board dts (if needed) and not in
the common dtsi?
The gcc-ipq4019.c clk driver has a fixed frequency table defining all
the valid frequencies. The reason why this "worked" in the past (i.e 4.9)
was a bug in the gcc-ipq4019.c driver that got fixed with:
"clk: qcom: ipq4019: Add the apss cpu pll divider clock node"
From what I can tell, back then the clk driver didn't really program
the P_DDRPLLAPSS clock so the device was left running at the
max frequency that u-boot or SBL1 programmed it.

Anyway, I took a peek into the patches that I sent to Mathias and John.
From what I can tell the 716.8 MHz to 716 MHz didn't happen there. But I
think I know where it comes from: You see "Sricharan R" posted this patch
to linux-msm-arm: <https://patchwork.kernel.org/patch/10303787/>. But please
check with Mathias too (CCd).

Thank you and best regards,
Christian

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