Re: [PATCH v2 1/9] i2c: prepare runtime PM support for I2C client devices

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Fri, Sep 13, 2013 at 07:30:55AM -0700, Kevin Hilman wrote:
> Mika Westerberg <mika.westerberg@linux.intel.com> writes:
> 
> > On Thu, Sep 12, 2013 at 02:34:21PM -0700, Kevin Hilman wrote:
> >> > diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> >> > index f32ca29..44374b4 100644
> >> > --- a/drivers/i2c/i2c-core.c
> >> > +++ b/drivers/i2c/i2c-core.c
> >> > @@ -248,11 +248,30 @@ static int i2c_device_probe(struct device *dev)
> >> >  					client->flags & I2C_CLIENT_WAKE);
> >> >  	dev_dbg(dev, "probe\n");
> >> >  
> >> > +	/* Make sure the adapter is active */
> >> > +	pm_runtime_get_sync(&client->adapter->dev);
> >> > +
> >> > +	/*
> >> > +	 * Enable runtime PM for the client device. If the client wants to
> >> > +	 * participate on runtime PM it should call pm_runtime_put() in its
> >> > +	 * probe() callback.
> >> > +	 */
> >> > +	pm_runtime_get_noresume(&client->dev);
> >> > +	pm_runtime_set_active(&client->dev);
> >> 
> >> Why the set_active here?
> >> 
> >> For hardware that is disabled/powered-off on startup, there will now be
> >> a mismatch between the hardware state an the RPM core state.
> >
> > The call to pm_runtime_get_noresume() should make sure that the device is
> > in active state (at least in state where it can access the bus) if I'm
> > understanding this right.
> 
> No, after _get_noresume(), nothing happens to the hardware.  It simply
> increments the usecount.  From pm_runtime.h:
> 
> static inline void pm_runtime_get_noresume(struct device *dev)
> {
> 	atomic_inc(&dev->power.usage_count);
> }
> 
> So after the _get_noresume() and _set_active() you're very likely to
> have a disconnect between the hardware state and what state RPM thinks
> the hardware is in.

Good point.

I suppose calling pm_runtime_get() here would work (and make the state
active in all case)? I used _noresume() here because at this point the
driver itself hasn't had change to install it's RPM hooks.