[EXT] Re: [PATCH v2] cpufreq: armada-37xx: forbid cpufreq for 1.2 GHz variant

Mon Aug 1 07:12:54 PDT 2022

Hello Elad and thank you for response!

This errata is already implemented in the kernel for a longer time by
Gregory's commit:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=61c40f35f5cd6f67ccbd7319a1722eb78c815989

There is also 20ms delay after L2/L3 to L1 state switch.

Any idea what could be wrong here? Or is something more than above
commit needed to correctly implement that errata?

On Monday 01 August 2022 14:01:07 Elad Nachman wrote:
> Hi Pali,
> 
> There is an errata for that.
> 
> "
> Switching from L2/L3 state (200/300 MHz) to L0 state (1200 MHz) requires sudden changes of VDD supply, and it
> requires time to stabilize the VDD supply. The solution is to use gradual switching from L2/L3 to L1 and then L1 to L0
> state.
> "
> 
> I would also add additional delay for the VDD supply stabilization.
> 
> FYI,
> 
> Elad.
> 
> -----Original Message-----
> From: Pali Rohár <pali at kernel.org> 
> Sent: Monday, August 1, 2022 3:36 PM
> To: Elad Nachman <enachman at marvell.com>; Wojciech Bartczak <wbartczak at marvell.com>
> Cc: Marek Behún <kabel at kernel.org>; Viresh Kumar <viresh.kumar at linaro.org>; Gregory CLEMENT <gregory.clement at bootlin.com>; Robert Marko <robert.marko at sartura.hr>; Tomasz Maciej Nowak <tmn505 at gmail.com>; Anders Trier Olesen <anders.trier.olesen at gmail.com>; Philip Soares <philips at netisense.com>; linux-pm at vger.kernel.org; Sebastian Hesselbarth <sebastian.hesselbarth at gmail.com>; linux-arm-kernel at lists.infradead.org; nnet <nnet at fastmail.fm>
> Subject: [EXT] Re: [PATCH v2] cpufreq: armada-37xx: forbid cpufreq for 1.2 GHz variant
> 
> External Email
> 
> ----------------------------------------------------------------------
> + Elad and Wojciech from Marvell
> 
> Could you please look at this issue and/or forward it to relevant Marvell team?
> 
> Maintainer Viresh already wrote that we cannot hang forever for Marvell and patch which disables support for 1.2 GHz was merged:
> https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_linux-2Dpm_20210809040224.j2rvopmmqda3utc5-40vireshk-2Di7_&d=DwIDaQ&c=nKjWec2b6R0mOyPaz7xtfQ&r=eTeNTLEK5-TxXczjOcKPhANIFtlB9pP4lq9qhdlFrwQ&m=5nMMKyKOOM3XdMe_PerZRx8L7-D7MkWhCl7GxpXTPiotVf1TR4j8v3bpjQmRKCLC&s=cXiCZByknfz1rOIgJl4fJHl1KLLRq2shHul2-VPpYP0&e= 
> 
> On Sunday 08 August 2021 21:30:26 Pali Rohár wrote:
> > Gentle reminder. This is really serious issue. Could you please look at it?
> > 
> > Adding more MarvellEmbeddedProcessors people to the loop: Evan, 
> > Benjamin an Igal
> > 
> > On Thursday 15 July 2021 21:33:21 Pali Rohár wrote:
> > > Ping! Gentle reminder for Marvell people.
> > > 
> > > On Thursday 08 July 2021 16:34:51 Pali Rohár wrote:
> > > > Konstantin, Nadav, Ken, Victor, Jason: This issue is pretty 
> > > > serious, CPU on 1.2GHz A3720 is crashing. Could you please look at it?
> > > > 
> > > > On Friday 02 July 2021 18:30:35 Pali Rohár wrote:
> > > > > +Jason from GlobalScale as this issue affects GlobalScale Espressobin Ultra and V7 1.2 GHz boards.
> > > > > 
> > > > > On Thursday 01 July 2021 00:56:01 Marek Behún wrote:
> > > > > > The 1.2 GHz variant of the Armada 3720 SOC is unstable with 
> > > > > > DVFS: when the SOC boots, the WTMI firmware sets clocks and 
> > > > > > AVS values that work correctly with 1.2 GHz CPU frequency, but 
> > > > > > random crashes occur once cpufreq driver starts scaling.
> > > > > > 
> > > > > > We do not know currently what is the reason:
> > > > > > - it may be that the voltage value for L0 for 1.2 GHz variant provided
> > > > > >   by the vendor in the OTP is simply incorrect when scaling is 
> > > > > > used,
> > > > > > - it may be that some delay is needed somewhere,
> > > > > > - it may be something else.
> > > > > > 
> > > > > > The most sane solution now seems to be to simply forbid the 
> > > > > > cpufreq driver on 1.2 GHz variant.
> > > > > > 
> > > > > > Signed-off-by: Marek Behún <kabel at kernel.org>
> > > > > > Fixes: 92ce45fb875d ("cpufreq: Add DVFS support for Armada 
> > > > > > 37xx")
> > > > > > ---
> > > > > > If someone from Marvell could look into this, it would be 
> > > > > > great since basically 1.2 GHz variant cannot scale, which is a 
> > > > > > feature that was claimed to be supported by the SOC.
> > > > > > 
> > > > > > Ken Ma / Victor Gu, you have worked on commit 
> > > > > > https://urldefense.proofpoint.com/v2/url?u=https-3A__github.co
> > > > > > m_MarvellEmbeddedProcessors_linux-2Dmarvell_commit_d6719fdc2b3
> > > > > > cac58064f41b531f86993c919aa9a&d=DwIDaQ&c=nKjWec2b6R0mOyPaz7xtf
> > > > > > Q&r=eTeNTLEK5-TxXczjOcKPhANIFtlB9pP4lq9qhdlFrwQ&m=5nMMKyKOOM3X
> > > > > > dMe_PerZRx8L7-D7MkWhCl7GxpXTPiotVf1TR4j8v3bpjQmRKCLC&s=b9cDKem
> > > > > > t70OiTJF6KXj0ySzbxpsB_nuteXJE87via80&e=
> > > > > > in linux-marvell.
> > > > > > Your patch takes away the 1202 mV constant for 1.2 GHz base 
> > > > > > CPU frequency and instead adds code that computes the voltages 
> > > > > > from the voltage found in L0 AVS register (which is filled in by WTMI firmware).
> > > > > > 
> > > > > > Do you know why the code does not work correctly for some 1.2 
> > > > > > GHz boards? Do we need to force the L0 voltage to 1202 mV if 
> > > > > > it is lower, or something?
> > > > > > ---
> > > > > >  drivers/cpufreq/armada-37xx-cpufreq.c | 6 +++++-
> > > > > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > > > > > 
> > > > > > diff --git a/drivers/cpufreq/armada-37xx-cpufreq.c 
> > > > > > b/drivers/cpufreq/armada-37xx-cpufreq.c
> > > > > > index 3fc98a3ffd91..c10fc33b29b1 100644
> > > > > > --- a/drivers/cpufreq/armada-37xx-cpufreq.c
> > > > > > +++ b/drivers/cpufreq/armada-37xx-cpufreq.c
> > > > > > @@ -104,7 +104,11 @@ struct armada_37xx_dvfs {  };
> > > > > >  
> > > > > >  static struct armada_37xx_dvfs armada_37xx_dvfs[] = {
> > > > > > -	{.cpu_freq_max = 1200*1000*1000, .divider = {1, 2, 4, 6} },
> > > > > > +	/*
> > > > > > +	 * The cpufreq scaling for 1.2 GHz variant of the SOC is currently
> > > > > > +	 * unstable because we do not know how to configure it properly.
> > > > > > +	 */
> > > > > > +	/* {.cpu_freq_max = 1200*1000*1000, .divider = {1, 2, 4, 6} 
> > > > > > +}, */
> > > > > >  	{.cpu_freq_max = 1000*1000*1000, .divider = {1, 2, 4, 5} },
> > > > > >  	{.cpu_freq_max = 800*1000*1000,  .divider = {1, 2, 3, 4} },
> > > > > >  	{.cpu_freq_max = 600*1000*1000,  .divider = {2, 4, 5, 6} },
> > > > > > --
> > > > > > 2.31.1
> > > > > > 