linux-kernel - Re: [PATCH 2/2] drm/rockchip: Convert the probe function to the generic drm_of_component

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Message-ID: <20151116165206.GC4158@e106497-lin.cambridge.arm.com>
Date:	Mon, 16 Nov 2015 16:52:06 +0000
From:	Liviu Dudau <Liviu.Dudau@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Mark Yao <mark.yao@...k-chips.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	David Airlie <airlied@...ux.ie>, Eric Anholt <eric@...olt.net>,
	linux-rockchip <linux-rockchip@...ts.infradead.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] drm/rockchip: Convert the probe function to the
 generic drm_of_component_probe()

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!

Liviu

> 
> Thanks.
> 
> -- 
> FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
> according to speedtest.net.
> 

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
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