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

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Date:   Wed, 4 Jan 2017 20:57:47 -0300
From:   Javier Martinez Canillas <javier@....samsung.com>
To:     Doug Anderson <dianders@...omium.org>,
        Krzysztof Kozlowski <krzk@...nel.org>
Cc:     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

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.

> -Doug

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America