ARM: dts: rockchip: add the MiQi board's fan definition

[Heiko Stuebner]

Hi Willy,

Am Samstag, 11. Februar 2017, 18:45:54 CET schrieb Willy Tarreau:
> On Sat, Feb 11, 2017 at 05:33:16PM +0100, Heiko Stuebner wrote:
> > Am Samstag, 11. Februar 2017, 09:56:55 CET schrieb Willy Tarreau:
> > > The MiQi board is sold with an enclosure in which a fan is connected
> > > to the second LED output, and configured by default in "heartbeat"
> > > mode so that it rotates slowly and increases when the CPU load
> > > increases, ensuring appropriate cooling by default. This LED output
> > > is called "Fan" in the original kernel and connected to GPIO18
> > > (gpiochip 0, pin 18). Here we called it "miqi:green:fan" to stay
> > > consistent with the kernel's naming conventions.
> > 
> > I tend to disagree with this approach. A fan is not a led and the
> > devicetree is about describing the hardware, not how a specific kernel
> > likes to use things> 
> > :-) .
> 
> Sure but I was trying to stay as close as possible to the intended
> purpose of the connector on the board as it is sold :-)
>
> > The kernel already has a gpio-fan driver (drivers/hwmon) or you could
> > resurrect the gpio-pwm patch [0] from Olliver Schinagl and use the pwm-fan
> > on top of that for more intermediate steps.
> 
> Ah it's great to know there has already been something like this because
> I thought about developing one for the same reason.
> 
> > > It's worth noting that without this patch the fan doesn't work at
> > > all, risking to make the board overheat.
> > 
> > At least cpufreq is already hooked to the thermal controller on the
> > rk3288, so even without additional cooling it should select lower cpu
> > frequencies keeping the heat in line and prevent overheating the board.
> 
> Well that's one way to see it, as for me throttling the CPU is the last
> resort before seeing it die ;

That's what I was trying to say :-) ... it won't overheat because cpufreq will 
throttle it as a last resort.


> I find it sad to waste all the performance
> of a 3288 that way, otherwise it's easier to use something like a dirt
> a much slower and cheaper cortex A5. But I agree with the point regarding
> the gpio-pwm.

Even with the gpio-fan you should see results if you simply add the fan as 
active trip point somewhere before the cpufreq trip points. So let the fan get 
activated at 50/60° or so.


Heiko

> I think that mqmaker initially designed the GPIO to be used
> as a led to benefit from the heartbeat trigger which more or less replaces
> what a more efficient thermal control could achieve.