linux-kernel - Re: [PATCH v3 2/2] ARM: dts: sun8i-r40: Add "cpu-supply" node for sun8i-r40 based board

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Date:   Fri, 13 May 2022 16:23:20 +0800
From:   qianfan <qianfanguijin@....com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     linux-sunxi@...ts.linux.dev, Rob Herring <robh+dt@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 2/2] ARM: dts: sun8i-r40: Add "cpu-supply" node for
 sun8i-r40 based board



在 2022/5/13 16:15, Maxime Ripard 写道:
> On Fri, May 13, 2022 at 03:48:50PM +0800, qianfan wrote:
>>
>> 在 2022/5/13 15:38, Maxime Ripard 写道:
>>> Hi,
>>>
>>> On Thu, May 12, 2022 at 03:18:58PM +0800, qianfanguijin@....com wrote:
>>>> From: qianfan Zhao <qianfanguijin@....com>
>>>>
>>>> sun8i-r40 actived cpufreq feature now, let's add "cpu-supply" node on
>>>> board.
>>>>
>>>> Signed-off-by: qianfan Zhao <qianfanguijin@....com>
>>>> ---
>>>>    arch/arm/boot/dts/sun8i-r40-bananapi-m2-ultra.dts | 4 ++++
>>>>    arch/arm/boot/dts/sun8i-r40-feta40i.dtsi          | 4 ++++
>>>>    arch/arm/boot/dts/sun8i-t3-cqa3t-bv3.dts          | 4 ++++
>>>>    arch/arm/boot/dts/sun8i-v40-bananapi-m2-berry.dts | 4 ++++
>>>>    4 files changed, 16 insertions(+)
>>>>
>>>> diff --git a/arch/arm/boot/dts/sun8i-r40-bananapi-m2-ultra.dts b/arch/arm/boot/dts/sun8i-r40-bananapi-m2-ultra.dts
>>>> index a6a1087a0c9b..4f30018ec4a2 100644
>>>> --- a/arch/arm/boot/dts/sun8i-r40-bananapi-m2-ultra.dts
>>>> +++ b/arch/arm/boot/dts/sun8i-r40-bananapi-m2-ultra.dts
>>>> @@ -113,6 +113,10 @@ &ahci {
>>>>    	status = "okay";
>>>>    };
>>>> +&cpu0 {
>>>> +	cpu-supply = <&reg_dcdc2>;
>>>> +};
>>>> +
>>> This will break bisection on those boards. Indeed, you added the OPPs on
>>> the first patch, and if you only apply that patch, the boards in the
>>> second patch will be missing their CPU regulator. The kernel will then
>>> ramp up the frequency to the highest OPP, but will not change the
>>> voltage, resulting in a crash.
>> This is a good point and I will merge those two patch.
> That's not what I meant to say. Those two patches are great separated.
> You can invert them though.
haha, invert them, so interesting. good idea.
>
>>> There's a similar issue for all the boards that don't have a regulator
>>> in the first place.
>>>
>>> The way we worked around this for the other SoCs is to have a DTSI with
>>> the OPPs with a frequency higher than what U-Boot boots with (1008MHz?),
>>> and only include that DTSI on boards that have a CPU regulator hooked in.
>> Is this really necessary? It seems like every board based on sun8i-r40
>> have a cpu regulator.
> This probably won't be the case whenever someone starts a new design,
> and then they'll face random crashes for no apparent reason, and waste a
> lot of time in the process.
>
> Whereas the alternative is that you would be missing some OPPs,
> something that is fairly easy to figure out.
How about remove the OPPs which greate that 1.08G in sun8i-r40.dtsi,
If some boards want to run at a higher frequency, can add them byself
in the board's file.
>
> Maxime