Re: [PATCH v2 4/4] cpufreq: mediatek: Raise proc and sram max voltage for MT7622/7623

[AngeloGioacchino Del Regno]

Il 23/05/23 19:37, Daniel Golle ha scritto:
> On Tue, May 23, 2023 at 04:56:47PM +0200, AngeloGioacchino Del Regno wrote:
> > Il 22/05/23 20:03, Daniel Golle ha scritto:
> > > Hi Jia-Wei,
> > > Hi AngeloGioacchino,
> > >
> > > On Fri, Mar 24, 2023 at 06:11:30PM +0800, jia-wei.chang wrote:
> > > > From: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
> > > >
> > > > During the addition of SRAM voltage tracking for CCI scaling, this
> > > > driver got some voltage limits set for the vtrack algorithm: these
> > > > were moved to platform data first, then enforced in a later commit
> > > > 6a17b3876bc8 ("cpufreq: mediatek: Refine mtk_cpufreq_voltage_tracking()")
> > > > using these as max values for the regulator_set_voltage() calls.
> > > >
> > > > In this case, the vsram/vproc constraints for MT7622 and MT7623
> > > > were supposed to be the same as MT2701 (and a number of other SoCs),
> > > > but that turned out to be a mistake because the aforementioned two
> > > > SoCs' maximum voltage for both VPROC and VPROC_SRAM is 1.36V.
> > > >
> > > > Fix that by adding new platform data for MT7622/7623 declaring the
> > > > right {proc,sram}_max_volt parameter.
> > > >
> > > > Fixes: ead858bd128d ("cpufreq: mediatek: Move voltage limits to platform data")
> > > > Fixes: 6a17b3876bc8 ("cpufreq: mediatek: Refine mtk_cpufreq_voltage_tracking()")
> > > > Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
> > > > Signed-off-by: Jia-Wei Chang <jia-wei.chang@xxxxxxxxxxxx>
> > > > ---
> > > >    drivers/cpufreq/mediatek-cpufreq.c | 13 +++++++++++--
> > > >    1 file changed, 11 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/cpufreq/mediatek-cpufreq.c b/drivers/cpufreq/mediatek-cpufreq.c
> > > > index 764e4fbdd536..9a39a7ccfae9 100644
> > > > --- a/drivers/cpufreq/mediatek-cpufreq.c
> > > > +++ b/drivers/cpufreq/mediatek-cpufreq.c
> > > > @@ -693,6 +693,15 @@ static const struct mtk_cpufreq_platform_data mt2701_platform_data = {
> > > >    	.ccifreq_supported = false,
> > > >    };
> > > > +static const struct mtk_cpufreq_platform_data mt7622_platform_data = {
> > > > +	.min_volt_shift = 100000,
> > > > +	.max_volt_shift = 200000,
> > > > +	.proc_max_volt = 1360000,
> > > > +	.sram_min_volt = 0,
> > > > +	.sram_max_volt = 1360000,
> > >
> > > This change breaks cpufreq (with ondemand scheduler) on my BPi R64
> > > board (having MT7622AV SoC with MT6380N PMIC).
> > > ...
> > > [    2.540091] cpufreq: __target_index: Failed to change cpu frequency: -22
> > > [    2.556985] cpu cpu0: cpu0: failed to scale up voltage!
> > > ...
> > > (repeating a lot, every time the highest operating point is selected
> > > by the cpufreq governor)
> > >
> > > The reason is that the MT6380N doesn't support 1360000uV on the supply
> > > outputs used for SRAM and processor.
> > >
> > > As for some reason cpufreq-mediatek tries to rise the SRAM supply
> > > voltage to the maximum for a short moment (probably a side-effect of
> > > the voltage tracking algorithm), this fails because the PMIC only
> > > supports up to 1350000uV. As the highest operating point is anyway
> > > using only 1310000uV the simple fix is setting 1350000uV as the maximum
> > > instead for both proc_max_volt and sram_max_volt.
> > >
> > > A similar situation applies also for BPi R2 (MT7623NI with MT6323L
> > > PMIC), here the maximum supported voltage of the PMIC which also only
> > > supports up to 1350000uV, and the SoC having its highest operating
> > > voltage defined at 1300000uV.
> > >
> > > If all agree with the simple fix I will post a patch for that.
> > >
> > > However, to me it feels fishy to begin with that the tracking algorithm
> > > tries to rise the voltage above the highest operating point defined in
> > > device tree, see here:
> > >
> > > 6a17b3876bc830 drivers/cpufreq/mediatek-cpufreq.c (Jia-Wei Chang              2022-05-05 19:52:20 +0800 100)    new_vsram = clamp(new_vproc + soc_data->min_volt_shift,
> > > 6a17b3876bc830 drivers/cpufreq/mediatek-cpufreq.c (Jia-Wei Chang              2022-05-05 19:52:20 +0800 101)                      soc_data->sram_min_volt, soc_data->sram_max_volt);
> > >
> > > However, I did not investigate in depth the purpose of this
> > > initial rise and can impossibly test my modifications to the
> > > tracking algorithm on all supported SoCs.
> >
> > Thanks for actually reporting that, I don't think that there's any
> > valid reason why the algorithm should set a voltage higher than the
> > maximum votage specified in the fastest OPP.
> >
> > Anyway - the logic for the platform data of this driver is to declare
> > the maximum voltage that SoC model X supports, regardless of the actual
> > board-specific OPPs, so that part is right; to solve this issue, I guess
> > that the only way is for this driver to parse the OPPs during .probe()
> > and then always use in the algorithm
> >
> > 	vproc_max = max(proc_max_volt, opp_vproc_max);
> > 	vsram_max = max(sram_max_volt, vsram_vreg_max);
>
> You probably meant to write
> vproc_max = min(proc_max_volt, opp_vproc_max);
> vsram_max = min(sram_max_volt, vsram_vreg_max);
>
> right?

Apparently, some of my braincells was apparently taking a break. :-)

Yes, I was meaning min(), not max() :-)

Cheers!

> > Jia-Wei, can you please handle this?
> >
> > Thanks,
> > Angelo