RE: [PATCH v2 RESEND] i2c: cadence: Add system suspend and resume PM support

[JiSheng Teoh <jisheng.teoh@starfivetech.com>]

Hi Andi,
> 
> ...
> 
> > > > +static int __maybe_unused cdns_i2c_resume(struct device *dev) {
> > > > +	struct cdns_i2c *xi2c = dev_get_drvdata(dev);
> > > > +	int err;
> > > > +
> > > > +	err = cdns_i2c_runtime_resume(dev);
> > > > +	if (err)
> > > > +		return err;
> > > > +
> > > > +	if (pm_runtime_status_suspended(dev)) {
> > > > +		err = cdns_i2c_runtime_suspend(dev);
> > > > +		if (err)
> > > > +			return err;
> > >
> > > We call the cdns_i2c_resume() functions to come up from a suspended
> > > state. But, if we fail to resume, we call the suspend and return '0' (because this always returns '0').
> > >
> > > In other words, if we take this path, we call resume, but we still end up suspended and return success.
> > >
> > > Andi
> > >
> >
> > My understanding is that during system level resume 'cdns_i2c_resume()', the i2c device itself can still be held in runtime suspend
> regardless of the change in system level PM.
> > Looking back at this, we invoke cdns_i2c_runtime_resume() to enable clock and init the i2c device, the runtime PM state is still
> unchanged and kept suspended.
> > pm_runtime_status_suspended() will be evaluated as true, and runtime suspend 'cdns_i2c_runtime_suspend()' is invoked to
> disable the clock. This balances the clock count enabled earlier.
> 
> If this is your issue, what if we do not enable the clock during resume? and we just mark the device as resumed?
> 
That will work as well. The i2c device will be runtime resumed again during cdns_i2c_master_xfer() anyway, but thought that it
would be a good idea to check if the i2c device is able runtime resume during a system level resume.

> > The runtime PM state is only resumed during cdns_i2c_master_xfer() through pm_runtime_resume_and_get(), and subsequently
> kept suspended through pm_runtime_put_autosuspend().
> > Since the cdns_i2c_runtime_suspend() always return '0', I will simplify them as follow:
> > +if (pm_runtime_status_suspended(dev))
> > +	cdns_i2c_runtime_suspend(dev);
> 
> I'd prefer checking the error value, even though we are sure on the expected return. It's more future proof.
> 
> Andi
> 
Ok, I will keep the original changes.

> > > > +	}
> > > > +
> > > > +	i2c_mark_adapter_resumed(&xi2c->adap);
> > > > +
> > > > +	return 0;
> > > > +}