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

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Date:	Mon, 16 Nov 2015 16:30:16 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Liviu Dudau <Liviu.Dudau@....com>
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()

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.

Thanks.

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