linux-kernel - Re: [PATCH v2 4/5] hwmon: (gxp_fan

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Date:   Fri, 2 Jun 2023 15:02:05 +0000
From:   "Hawkins, Nick" <nick.hawkins@....com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Linus Walleij <linus.walleij@...aro.org>
CC:     "Verdun, Jean-Marie" <verdun@....com>,
        "brgl@...ev.pl" <brgl@...ev.pl>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "jdelvare@...e.com" <jdelvare@...e.com>,
        "andy.shevchenko@...il.com" <andy.shevchenko@...il.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>
Subject: Re: [PATCH v2 4/5] hwmon: (gxp_fan_ctrl) Provide fan info via gpio

> > 
> > This can be done several ways, the most straight-forward is notifiers.
> > include/linux/notifier.h
> > 

> This is all unnecessary. The hwmon driver could register a gpio pin,
> including interrupt, and then report state changes to userspace with
> sysfs or udev events on the registered hwmon sysfs attributes.

> If they really want to use userspace for everything, they should
> just use userspace for everything and not bother with a kernel driver.

Greetings Guenter and Linus,

Thank you for your feedback and assistance. I discussed this with my
team and the direction they are leaning is that they want to own the
GPIOs in user space. The fan driver it would still need to be used
to set and read PWMs as they are kernel protected registers. It will
also need to be there to coordinate the proper offset in the GXP
registers to control a particular fans PWM.

For hot pluggable devices such as fans and psu they will need to
bind/unbind the hwmon driver of the device as it is inserted/removed.

Is this an acceptable path forward?

If it is I will revise this patchset once more to make the fan independent
of the GPIO driver.

Thanks again for all the guidance,

-Nick Hawkins