Messages in this thread | | | Subject | Re: [PATCH V2 3/9] dt-bindings: Tegra186 tachometer device tree bindings | From | Mikko Perttunen <> | Date | Mon, 9 Apr 2018 17:37:09 +0300 |
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On 04/09/2018 04:21 PM, Rob Herring wrote: > On Mon, Apr 9, 2018 at 12:38 AM, Mikko Perttunen <cyndis@kapsi.fi> 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.
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).
> > 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. Or are you complaining about the nvidia,pulse-per-rev/capture-window-len properties?
Thanks, Mikko
> > Rob > >> >> Thanks, >> Mikko >> >> >> On 03/27/2018 05:52 PM, Rob Herring wrote: >>> >>> On Wed, Mar 21, 2018 at 10:10:38AM +0530, Rajkumar Rampelli wrote: >>>> >>>> Supply Device tree binding documentation for the NVIDIA >>>> Tegra186 SoC's Tachometer Controller >>>> >>>> Signed-off-by: Rajkumar Rampelli <rrajk@nvidia.com> >>>> --- >>>> >>>> V2: Renamed compatible string to "nvidia,tegra186-pwm-tachometer" >>>> Renamed dt property values of clock-names and reset-names to >>>> "tachometer" >>>> from "tach" >>> >>> >>> Read my prior comments on v1. >>> >>> Rob >>> -- >>> To unsubscribe from this list: send the line "unsubscribe linux-tegra" in >>> the body of a message to majordomo@vger.kernel.org >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>> >> -- >> To unsubscribe from this list: send the line "unsubscribe devicetree" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html
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