linux-kernel - Re: [PATCH v7 1/3] dt-bindings: hwmon: Add adt7475 fan/pwm properties

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Message-ID: <afiirmp4q4txm5ibiaa4nvzl6tlj7merc3ienvt4o4zhmbcuua@f6r6fyg2jviz>
Date: Tue, 3 Jun 2025 10:20:17 +0200
From: Uwe Kleine-König <ukleinek@...nel.org>
To: Chris Packham <Chris.Packham@...iedtelesis.co.nz>
Cc: "jdelvare@...e.com" <jdelvare@...e.com>, 
	"linux@...ck-us.net" <linux@...ck-us.net>, "robh@...nel.org" <robh@...nel.org>, 
	"krzk+dt@...nel.org" <krzk+dt@...nel.org>, "conor+dt@...nel.org" <conor+dt@...nel.org>, 
	"linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>, "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>
Subject: Re: [PATCH v7 1/3] dt-bindings: hwmon: Add adt7475 fan/pwm properties

Hello Chris,

On Mon, Jun 02, 2025 at 08:52:56PM +0000, Chris Packham wrote:
> On 30/05/2025 21:38, Uwe Kleine-König wrote:
> > I wonder how other similar devices determine the default duty cycle.
> > Isn't the norm to make the fan rotate at max speed and then when
> > userspace takes over it's speeded down?
> 
> Yes that is the normal (and sensible thing do to). But occasionally 
> hardware designers like to use incredibly over spec'd  fans that are 
> just ridiculously noisy. On some products I've worked on we added basic 
> fan control to u-boot so we could silence the fans early in the boot. I 
> also gather that in the PC world the fan control is often done 
> externally to the OS. In the specific case were I needed this 
> functionality it was an embedded x86_64 so I had neither U-Boot nor a BMC.

So you're saying that Linux is the first instance that is able to setup
the fan -- no BIOS, right?

I think that's quite normal and the fan is only noisy until userspace
takes over. So I still think that is what should happen here.

In case this is really too noisy, I'd prefer the driver to know itself
how to setup the fan and not put that policy into the device tree.

Best regards
Uwe

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