linux-kernel - Re: [PATCH] arm64: dts: meson: Enable active coling using gpio-fan on Odroid N2/N2+

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Date:   Thu, 20 Oct 2022 10:15:17 +0200
From:   neil.armstrong@...aro.org
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Anand Moon <linux.amoon@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: meson: Enable active coling using gpio-fan on
 Odroid N2/N2+

On 19/10/2022 22:40, Martin Blumenstingl wrote:
> Hi Anand,
> 
> On Wed, Oct 19, 2022 at 7:17 PM Anand Moon <linux.amoon@...il.com> wrote:
> [...]
>>>> +&pwm_AO_ab {
>>>
>>> &pwm_AO_cd not _ab
>>>
>> No it has a conflict with CPU_B (vddcpu_b) PWM
> Uh, you're right. That's probably why the Hardkernel team uses a
> software based PWM implementation: [0]
> In hindsight they should have used a different pad either for VDDCPU_B
> or the fan.
> 
> I think the most pragmatic approach (since the "GPIO PWM" driver is
> not upstream and I don't know if something like that would be accepted
> upstream) is to use a GPIO based fan as you did in your initial patch.
> Not sure what others think though.
> 

Indeed I recall them using a SW pwm.

Yes it's perfectly ok to use a gpio-fan.

Anand, please fixup the ddr-active name and send a v2.

Thanks,
Neil

> 
> Best regards,
> Martin
> 
> 
> [0] https://github.com/hardkernel/linux/blob/c109dec94e7e819554830acfac4b6ed96e230179/arch/arm64/boot/dts/amlogic/meson64_odroidn2.dtsi#L356-L359