mvebu: armada 3720 cpufreq reverts

[Marek Behun]

On Wed, 30 Jun 2021 17:51:24 +0200
Robert Marko <robert.marko at sartura.hr> wrote:

> On Wed, Jun 30, 2021 at 3:19 PM Marek Behún <marek.behun at nic.cz> wrote:
> >
> > Hello Robert,
> >
> > I am writing regarding commit
> >   mvebu: 5.10 fix DVFS caused random boot crashes
> >   https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=080a0b74e39d159eecf69c468debec42f28bf4d8
> > in OpenWRT.
> >
> > This commit reverts the one patch of a3720 cpufreq driver, but not
> > the subsequent ones.
> >
> > Your commit message says that some 1.2 GHz SOCs are unstable with the
> > fix. Did you also test this with the subsequent patches, which are now
> > in stable kernels? I guess the answer is yes, because all these patches
> > were backported to 5.10.37.  
> 
> Hi Marek,
> 
> Yes, the rest of the patches were there as well.
> >
> > I am of the opinion that a better approach would be to
> > - either disable cpufreq for 1.2 GHz variants
> > - fix a3720 cpufreq driver to only scale up to 1 GHz on 1.2 GHz variant  
> 
> I would prefer limiting it to 1GHz as that would not cause performance issues,
> but 1GHz models could have the same issue as well.
> This is because the voltages that are set as a minimum are from the testing that
> Pali and the Turris guys did, but it really depends on the SoC batch
> you receive.
> >
> > Since the approach you've taken now (reverting the patch) basically
> > changes the CPU parnet clock to DDR clock, which is just wrong.
> > Worse is that you are doing this for everybody, not just for the 1.2
> > GHz variants.
> >
> > What do you think?  
> 
> I understand that it was not the best solution, but something had to be done as
> I was not able to even finish booting on multiple boards before crashing.
> It just reverted the things back to the previous state.
> 
> I really could not figure a proper solution even after being in touch
> with Pali, and contacting
> GlobalScale.
> 
> This is an issue caused by Marvell simply ignoring the issue and
> refusing to publish
> a fix or release the OTP and AVS docs as they all have a validated
> voltage in the OTP
> somewhere.

Robert, we've found this table in linux-marvell repository:
  https://github.com/MarvellEmbeddedProcessors/linux-marvell/blob/dc33b62c90696afb6adc7dbcc4ebbd48bedec269/drivers/regulator/armada-37xx-regulator.c#L99-L105

Do you still have the 1.2 GHz boards which were crashing? Would you be
willing to test whether those boards are stable if we provided patch
for you?

Marek