Re: [PATCH 2/2] drm/rockchip: Convert the probe function to the generic drm_of_component_probe()

["Heiko Stübner" <heiko@sntech.de>]

Am Montag, 16. November 2015, 16:52:06 schrieb Liviu Dudau:
> On Mon, Nov 16, 2015 at 04:30:16PM +0000, Russell King - ARM Linux wrote:
> > I've tweaked your patch to make the above (buggy) change a little clearer.
> > 
> > On Mon, Nov 16, 2015 at 02:44:53PM +0000, Liviu Dudau wrote:
> > > -	for (i = 0;; i++) {
> > > -		port = of_parse_phandle(np, "ports", i);
> > > -		if (!port)
> > > -			break;
> > > -
> > > -		if (!of_device_is_available(port->parent)) {
> > > -			of_node_put(port);
> > > -			continue;
> > > -		}
> > > 
> > > -		component_match_add(dev, &match, compare_of, port->parent);
> > > -		of_node_put(port);
> > > -	}
> > > 
> > > -static int compare_of(struct device *dev, void *data)
> > > -{
> > > -	struct device_node *np = data;
> > > -
> > > -	return dev->of_node == np;
> > > -}
> > 
> > The original above passes port->parent to component_match_add().  This
> > means 'np' in the above compare_of() function is 'port->parent'.
> > 
> > This means the above comparison is effectively:
> > 	dev->of_node == port->parent
> > 
> > The generic code instead does this:
> >                 component_match_add(dev, &match, compare_of, port);
> > 
> > So what we get in the comparison function is 'port' rather than
> > 
> > 'port->parent':
> > > +static int compare_port(struct device *dev, void *data)
> > > 
> > >  {
> > > 
> > > +	struct device_node *np = data;
> > > +	return dev->parent->of_node == np;
> > > +}
> > 
> > which means the comparison is:
> > 	dev->parent->of_node == port
> > 
> > which is a different comparison from the above.
> > 
> > You instead want this to be:
> > 	return dev->of_node == np->parent;
> > 
> > Heiko, please test the above change to compare_port() - I think you'll
> > find that will fix your issue.
> 
> Sorry, I admit I'm not very good at doing patches without being able
> to test them. :(
> 
> Thanks for helping on this!

Russell's hint was correct. With the compare function changed like he pointed 
out, I again get a working display with your patches :-)

So, thanks Russell for spotting this.


Heiko