linux-kernel - Re: [PATCH v2] ARM: dts: Add missing CPU frequencies for Exynos5422/5800

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Message-ID: <20170105194059.bwpotpv3zjtvg5oz@kozik-lap>
Date:   Thu, 5 Jan 2017 21:40:59 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Javier Martinez Canillas <javier@....samsung.com>
Cc:     Doug Anderson <dianders@...omium.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Kukjin Kim <kgene@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Andreas Faerber <afaerber@...e.de>,
        Thomas Abraham <thomas.ab@...sung.com>,
        Ben Gamari <ben@...rt-cactus.org>,
        Arjun K V <arjun.kv@...sung.com>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] ARM: dts: Add missing CPU frequencies for
 Exynos5422/5800

On Wed, Jan 04, 2017 at 08:57:47PM -0300, Javier Martinez Canillas wrote:
> Hello Doug,
> 
> On 01/04/2017 06:05 PM, Doug Anderson wrote:
> > Hi,
> > 
> > On Thu, Dec 29, 2016 at 6:17 AM, Krzysztof Kozlowski <krzk@...nel.org> wrote:
> >> On Thu, Dec 15, 2016 at 04:54:30PM -0800, Doug Anderson wrote:
> >>>> Index: b/arch/arm/boot/dts/exynos5800.dtsi
> >>>> ===================================================================
> >>>> --- a/arch/arm/boot/dts/exynos5800.dtsi 2016-12-15 12:43:54.365955950 +0100
> >>>> +++ b/arch/arm/boot/dts/exynos5800.dtsi 2016-12-15 12:43:54.361955949 +0100
> >>>> @@ -24,6 +24,16 @@
> >>>>  };
> >>>>
> >>>>  &cluster_a15_opp_table {
> >>>> +       opp@...0000000 {
> >>>> +               opp-hz = /bits/ 64 <2000000000>;
> >>>> +               opp-microvolt = <1250000>;
> >>>> +               clock-latency-ns = <140000>;
> >>>> +       };
> >>>> +       opp@...0000000 {
> >>>> +               opp-hz = /bits/ 64 <1900000000>;
> >>>> +               opp-microvolt = <1250000>;
> >>>> +               clock-latency-ns = <140000>;
> >>>> +       };
> >>>
> >>> I don't think the voltages you listed are high enough for all peach pi
> >>> boards for A15 at 1.9 GHz and 2.0 GHz, at least based on the research
> >>> I did.  See my response to v1.
> >>
> >> I wanted to apply this but saw this remaining issue. Javier tested it
> >> on Peach Pi so is this concern still valid?
> > 
> > I'm not sure.  It's been years since I did anything with exynos, so I
> > won't stand in the way if everyone else agrees that this patch is
> > good, but I will point out that testing on a single Peach Pi board is
> > not really enough given the massive difference in voltage needed
> > between the highest ASV group and the lowest (a whopping 112.5 mV from
> > looking in the Chrome OS source tree).
> > 
> 
> I agree. That's why answered that I wasn't able to find regressions on the
> Peach Pi I've access to, but I couldn't provide a Reviewed-by tag since it
> wasn't clear to me that the values were safe for any Exynos5420/5422/5800.

The value of 1.250 V seems to be covering only half of ASV values for
2.0 GHz so indeed it might be insufficient for some of the chips.
Unfortunately...

Best regards,
Krzysztof