On Mon, Apr 9, 2018 at 9:37 AM, Mikko Perttunen <cyndis@xxxxxxxx> wrote: > > > On 04/09/2018 04:21 PM, Rob Herring wrote: >> >> On Mon, Apr 9, 2018 at 12:38 AM, Mikko Perttunen <cyndis@xxxxxxxx> wrote: >>> >>> Rob, >> >> >> Please don't top post to lists. >> >>> this binding is for a specific IP block (for measuring/aggregating input >>> pulses) on the Tegra186 SoC, so I don't think it fits into any generic >>> binding. >> >> >> What is it hooked up to to measure? You only mention "fan" five times >> in the doc. > > > In practice, fans. > >> >> You have #pwm-cells too, so this block has PWM output as well? If not, >> then where's the PWM for the fan control because there is no point in >> having fan tach without some control mechanism. > > > It doesn't provide a PWM output. The (Linux) PWM framework provides > functionality in both directions - control and capture. But if the device > tree #pwm-cells/pwms properties are only for control, we may need to > introduce a new #capture-pwm-cells/capture-pwms or similar. Yes, perhaps. But there is no point in having #capture-pwm-cells/capture-pwms if you aren't describing the connection between the fan and the fan controller. > The idea is that the generic fan node can then specify two pwms, one for > control and one for capture, to enable e.g. closed-loop control (I'm not > personally familiar with the usecase for this but I could imagine something > like that). The control PWM can be something completely different, maybe not > a PWM in the first place (e.g. some fixed voltage). Yes. As you can have different types of fans (3-wire, 4-wire, etc.) they would have different compatibles and differing properties associated with them. >> There's only so many ways to control fans and types of fans, so yes, >> the interface of control and feedback lines between a fan and its >> controller should absolutely be generic. > > > I'm not quite getting what you mean by this. Clearly we need a custom > compatibility string for the tachometer as it's a different hardware block > with different programming than others. Yes, of course. It's the interface between fan controllers and fans that I'm concerned about. > Or are you complaining about the > nvidia,pulse-per-rev/capture-window-len properties? Well, those sound like properties of a fan (at least the first one), so they belong in a fan node. The aspeed fan controller is probably the closest thing we have to a fan binding. Look at that if you haven't already. Rob -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
