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

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Message-ID: <CAMpxmJUG+7ENUCnooexWKMwoq+zCuRsV_Y54un7omumk9nJguA@mail.gmail.com>
Date:   Mon, 15 Apr 2019 13:54:58 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Sekhar Nori <nsekhar@...com>
Cc:     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>,
        Adam Ford <aford173@...il.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

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).

Bart