Re: [PATCH v2 4/5] hwmon: (gxp_fan_ctrl) Provide fan info via gpio

[Linus Walleij <linus.walleij@linaro.org>]

On Thu, Jun 1, 2023 at 5:48 PM Hawkins, Nick <nick.hawkins@hpe.com> wrote:

> Thank you for your valuable feedback with the solutions you have provided.
> Before I proceed though I have a quick query about the fan driver.
> If I were to let the user space "own" gpio pins, would it be permissible for
> the userspace to feed a kernel driver data via sysfs?
>
> Ex:
> GPIO Driver -> (OpenBMC) -> Fandriver (sysfs).
>
> Here the GPIO driver would provide fan presence information to OpenBMC
> and then OpenBMC would provide fan presence info to the fan driver.

But why? Don't be so obsessed about userspace doing stuff using
sysfs, usually it is a better idea to let the kernel handle hardware.

I think this is a simple thermal zone you can define in the device
tree as indicated in my previous comment.

> If it were permissible to provide data to the driver via this method I could
> apply it to the PSU driver as well. the PSU driver which requires presence
> info to verify a PSU is inserted / removed.

It feels like you are looking for a way for two drivers to communicate
with each other.

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

Yours,
Linus Walleij