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

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Date:   Fri, 21 Oct 2022 10:38:48 +0200
From:   neil.armstrong@...aro.org
To:     Anand Moon <linux.amoon@...il.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.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 21/10/2022 07:07, Anand Moon wrote:
> Hi Martin / Neil,
> 
> On Thu, 20 Oct 2022 at 02:10, Martin Blumenstingl
> <martin.blumenstingl@...glemail.com> 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.
>>
> 
> When I use gpio-fan  I get the following output with gpioinfo
> Feature it woks as expected.
> 
> $ .sudo gpioinfo
> ....
> gpiochip1 - 15 lines:
>          line   0:      unnamed       unused   input  active-high
>          line   1:      unnamed       unused   input  active-high
>          line   2:      unnamed     "enable"  output  active-high [used]
>          line   3:      unnamed       unused   input  active-high
>          line   4:      unnamed       unused  output  active-high
>          line   5:      unnamed       unused   input  active-high
>          line   6:      unnamed       unused   input  active-high
>          line   7:      unnamed       unused   input  active-high
>          line   8:      unnamed "regulator-tflash_vdd" output active-high [used]
>          line   9:      unnamed      "TF_IO"  output  active-high [used]
>          line  10:      unnamed   "gpio-fan"  output  active-high [used]
>          line  11:      unnamed    "n2:blue"  output  active-high [used]
>          line  12:      unnamed       unused   input  active-high
>          line  13:      unnamed       unused   input  active-high
>          line  14:      unnamed       unused   input  active-high
> 
> When I am using pwm-fan using *pwm_ao_d_10_pins* pin is not getting
> registered below hence it is not working on my end.

It's expected because it's not used as a GPIO but another function, you should look
in the pinctrl debugfs files to see it.

> 
> $ .sudo gpioinfo
> ....
> gpiochip1 - 15 lines:
>          line   0:      unnamed       unused   input  active-high
>          line   1:      unnamed       unused   input  active-high
>          line   2:      unnamed     "enable"  output  active-high [used]
>          line   3:      unnamed       unused   input  active-high
>          line   4:      unnamed       unused  output  active-high
>          line   5:      unnamed       unused   input  active-high
>          line   6:      unnamed       unused   input  active-high
>          line   7:      unnamed       unused   input  active-high
>          line   8:      unnamed "regulator-tflash_vdd" output active-high [used]
>          line   9:      unnamed      "TF_IO"  output  active-high [used]
>          line  10:      unnamed       unused  output  active-high
>          line  11:      unnamed    "n2:blue"  output  active-high [used]
>          line  12:      unnamed       unused   input  active-high
>          line  13:      unnamed       unused   input  active-high
>          line  14:      unnamed       unused   input  active-high
> 
> Thanks
> -Anand
> 
> 
> 
> 
>>
>> Best regards,
>> Martin
>>
>>
>> [0] https://github.com/hardkernel/linux/blob/c109dec94e7e819554830acfac4b6ed96e230179/arch/arm64/boot/dts/amlogic/meson64_odroidn2.dtsi#L356-L359