[PATCH 2/2] realtek: add support for HPE 1920-24G-PoE-370w

[Tim Small]

Hi Evan,

Thanks for your email...

On 21/09/2024 15:06, Evan Jobling wrote:

> I had a look into this on JG922A today.
> I can set the fans to max on initialisation of RTL8231 using gpio-hog.
> But it not only is setting initalisation, it also 'hogs' it per description.
> 
> So that basically locks out gpio-fan or userspace setting it.

My thoughts were that the kernel's gpio-init code for that SoC shouldn't 
reset the gpio state - rather it should leave it in the state that the 
firmware configured it.  gpio-fan would then do the right thing.

> JG922A and JG928A got accepted without max fans by default?
> So I hope moving to hwmon and gpio-fan is sufficient?

I think that was probably a mistake - since there is definitely scope 
for hardware damage (conceivably even fire) with what is now the default 
OpenWRT behaviour for these devices.

This problem is gnarly unfortunately.

I think the only really "correct" ways to proceed are either to allow 
user control (defaulting to high speed i.e. delegating the decision), or 
to re-implement the same fan control algorithm as the OEM firmware does.

That algorithm could probably be discovered by treating it as a black 
box (e.g. giving it different PoE power loads, and/or operating 
temperatures, simulating fan failures etc. and observing behaviour).

Unfortunately I think that without access to the hardware specs and/or 
carrying out a lot of hardware characterisation work there is too much 
guesswork involved in implementing any other algorithm.

Tim.

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