linux-kernel - Re: [PATCH 2/5] drm: of: introduce drm_of_find_panel_or

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Message-ID: <20170206165323.255ltzlzmpfx4vl7@rob-hp-laptop>
Date:   Mon, 6 Feb 2017 10:53:23 -0600
From:   Rob Herring <robh@...nel.org>
To:     Philipp Zabel <p.zabel@...gutronix.de>,
        Liviu Dudau <liviu.dudau@....com>
Cc:     David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Sean Paul <seanpaul@...omium.org>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Frank Rowand <frowand.list@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Archit Taneja <architt@...eaurora.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Inki Dae <inki.dae@...sung.com>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Javier Martinez Canillas <javier@....samsung.com>,
        Stefan Agner <stefan@...er.ch>,
        Alison Wang <alison.wang@...escale.com>,
        Xinliang Liu <z.liuxinliang@...ilicon.com>,
        Rongrong Zou <zourongrong@...il.com>,
        Xinwei Kong <kong.kongxinwei@...ilicon.com>,
        Chen Feng <puck.chen@...ilicon.com>,
        CK Hu <ck.hu@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Marek Vasut <marex@...x.de>,
        Mark Yao <mark.yao@...k-chips.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Mali DP Maintainers <malidp@...s.arm.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Carlo Caione <carlo@...one.org>,
        Kevin Hilman <khilman@...libre.com>,
        Rob Clark <robdclark@...il.com>, Jyri Sarha <jsarha@...com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Eric Anholt <eric@...olt.net>,
        Russell King <rmk+kernel@...linux.org.uk>
Subject: Re: [PATCH 2/5] drm: of: introduce drm_of_find_panel_or_bridge

On Mon, Feb 06, 2017 at 11:42:48AM +0100, Philipp Zabel wrote:
> On Fri, 2017-02-03 at 21:36 -0600, Rob Herring wrote:
> > Many drivers have a common pattern of searching the OF graph for either an
> > attached panel or bridge and then finding the DRM struct for the panel
> > or bridge. Also, most drivers need to handle deferred probing when the
> > DRM device is not yet instantiated. Create a common function,
> > drm_of_find_panel_or_bridge, to find the connected node and the
> > associated DRM panel or bridge device.

[...]

> > +int drm_of_find_panel_or_bridge(const struct device_node *np,
> > +				int port, int endpoint,
> > +				struct drm_panel **panel,
> > +				struct drm_bridge **bridge)
> > +{
> > +	int ret = -ENODEV;
> 
> This is only returned if !panel && !bridge. I'd consider this invalid
> usage of this function, so maybe use -EINVAL?

Yes.

> > +	struct device_node *remote;
> > +
> > +	remote = of_graph_get_remote_node(np, port, endpoint);
> > +	if (!remote)
> > +		return -ENODEV;
> > +
> > +	if (bridge)
> > +		*bridge = NULL;
> 
> I would move this ^ ...
> 
> > +	if (panel) {
> > +		*panel = of_drm_find_panel(remote);
> > +		if (*panel) {
> 
> ... here.

Okay.

> > +			ret = 0;
> > +			goto out_put;
> > +		}
> > +		ret = -EPROBE_DEFER;
> > +	}
> > +
> > +	if (bridge) {
> > +		*bridge = of_drm_find_bridge(remote);
> > +		if (*bridge)
> > +			ret = 0;
> > +		else
> > +			ret = -EPROBE_DEFER;
> > +	}
> > +out_put:
> > +	of_node_put(remote);
> > +	return ret;
> > +}

I've ended up re-writing things a bit getting rid of the goto and the 
result looks like this:

int drm_of_find_panel_or_bridge(const struct device_node *np,
				int port, int endpoint,
				struct drm_panel **panel,
				struct drm_bridge **bridge)
{
	int ret = -EPROBE_DEFER;
	struct device_node *remote;

	if (!panel && !bridge)
		return -EINVAL;

	remote = of_graph_get_remote_node(np, port, endpoint);
	if (!remote)
		return -ENODEV;

	if (panel) {
		*panel = of_drm_find_panel(remote);
		if (*panel) {
			if (bridge)
				*bridge = NULL;
			ret = 0;
		}
	}

	/* No panel found yet, check for a bridge next. */
	if (ret && bridge) {
		*bridge = of_drm_find_bridge(remote);
		if (*bridge)
			ret = 0;
	}

	of_node_put(remote);
	return ret;
}