Re: [PATCH v2 3/5] counter: new TI eQEP driver

[David Lechner]

On 8/11/19 4:23 AM, Jonathan Cameron wrote:
> On Wed,  7 Aug 2019 14:40:21 -0500
> David Lechner <david@xxxxxxxxxxxxxx> wrote:
> > +
> > +	pm_runtime_enable(dev);
> > +	pm_runtime_get(dev);
> I'm a little confused on the flow here.
>
> pm_runtime_enable turns on runtime pm in general.
>
> pm_runtime_get basically calls runtime_resume to ensrue the
> device has power.
>
> > +
> > +	return devm_counter_register(dev, &priv->counter);
>
> This registers the userspace interfaces and exposes the device.
>
> > +}
> > +
> > +static int ti_eqep_remove(struct platform_device *pdev)
> > +{
> > +	struct device *dev = &pdev->dev;
> > +
> > +	pm_runtime_put(dev),
> > +	pm_runtime_disable(dev);
>
> pm_runtime_put notifies the system that the device is idle
> (and hence potentially turns it off).
>
> Not good if the counter is still registered.
>
> I'm assuming the presence of runtime pm at all is to interact
> with a parent driver and hence stop that turning off if this
> driver is probed?  That's probably fine, but add a few comments
> to make it clear that this driver itself doesn't really do
> runtime pm at all.

To be honest, despite reading the runtime PM docs more than once,
I still don't feel like I have a good grasp on how it is supposed
to work. I just know that we get a crash if it is omitted because
the IP block is not powered on.

I will fix the ordering in _remove() and add a comment in v3.