linux-kernel - Re: [PATCH v3 1/3] ARM: dts: da850: add cpu node and operating points to DT

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Message-ID: <CAHCN7xLyiKjr9dvVKBHmpacTQnWwdf_WjJ4xa-URrO8=-=UVQw@mail.gmail.com>
Date:   Mon, 15 Apr 2019 08:02:10 -0500
From:   Adam Ford <aford173@...il.com>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     Sekhar Nori <nsekhar@...com>, Bartosz Golaszewski <brgl@...ev.pl>,
        Kevin Hilman <khilman@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        David Lechner <david@...hnology.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] ARM: dts: da850: add cpu node and operating points
 to DT

On Mon, Apr 15, 2019 at 6:55 AM Bartosz Golaszewski
<bgolaszewski@...libre.com> wrote:
>
> pon., 15 kwi 2019 o 12:21 Sekhar Nori <nsekhar@...com> napisał(a):
> >
> > On 12/04/19 9:01 PM, Bartosz Golaszewski wrote:
> > > pt., 12 kwi 2019 o 15:53 Sekhar Nori <nsekhar@...com> napisał(a):
> > >>
> > >> On 12/04/19 5:41 PM, Bartosz Golaszewski wrote:
> > >>> pt., 12 kwi 2019 o 13:26 Sekhar Nori <nsekhar@...com> napisał(a):
> > >>>>
> > >>>> Hi Bartosz,
> > >>>>
> > >>>> On 08/04/19 1:29 PM, Bartosz Golaszewski wrote:
> > >>>>> From: David Lechner <david@...hnology.com>
> > >>>>>
> > >>>>> This adds a cpu node and operating points to the common da850.dtsi file.
> > >>>>>
> > >>>>> Additionally, a regulator is added to the LEGO EV3 board along with
> > >>>>> some board-specific CPU configuration.
> > >>>>>
> > >>>>> Regulators need to be hooked up on other boards to get them working.
> > >>>>>
> > >>>>> Signed-off-by: David Lechner <david@...hnology.com>
> > >>>>> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
> > >>>>
> > >>>> I remember you mentioning about some problems using OCHI and cpufreq
> > >>>> together. Are those resolved now? CPU PLL on DA850 can affect other
> > >>>> peripheral clock frequencies too. So enabling it should really be a
> > >>>> per-board decision.
> > >>>>
> > >>>
> > >>> The problems are still there. I've never been able to find the
> > >>> culprit, but it also occurs on TI BSP in the same way (a couple
> > >>> cpufreq transitions will make the controller unresponsive).
> > >>
> > >> Is that on LCDK as well? As I recall cpufreq was never enabled on LCDK
> > >> in TI BSP.
> > >>
> > >
> > > Yes, I just verified that the bug occurs on LCDK with patches from this series.
> > >
> > >> If the OHCI problem is present on LCDK, then there is a user visible
> > >> regression on mainline after this patch. Lets enable cpufreq in LCDK
> > >> only if all working peripherals keep working afterwards.
> > >>
> > >
> > > The OHCI driver doesn't register any cpufreq transition notifier
> > > callbacks. I can't really find anything in the datasheet, but I'm
> > > wondering if we shouldn't do something similar to what the driver for
> > > davinci i2c controller does. I'll try a couple things tomorrow.
> >
> > Even if OHCI issue is fixed, with a fixed regulator like on LCDK, I am
> > not sure the benefits of just frequency scaling will be justifiable enough.
> >
> > Fixing the OHCI issue may help in other boards like da850-evm use it
> > though. So that will be a good thing.
> >
> > How do you feel about keeping all OPPs disabled by default in da850.dtsi
> > and enabling only the ones that make sense for a board in <board>.dts?
> >
> > Empty OPP table is illegal, so this does mean that every board must
> > enable at least one OPP.
> >
>
> I guess in that case we'd need to make 300 MHz the default for
> da850-evm, but on da850-lcdk I'd go for 456 MHz (due to the regulator
> being fixed anyway).

Based on what I've seen of your V4 patch, I think it's fine to let the
da850-evm run at 375.  I am not sure why it would need to be default
to 300.
I agree that the cpu-supply is correctly referencing vdcdc3_reg, and
it's currently setup to handle .95 to 1.35V, which I think is OK based
on what I've seen and the OPP's look right from what I can tell.

adam
>
> Bart