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

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Date:   Mon, 06 Feb 2017 18:45:34 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Rob Herring <robh@...nel.org>
Cc:     Liviu Dudau <liviu.dudau@....com>, 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, 2017-02-06 at 10:53 -0600, Rob Herring wrote:
> 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:

Looks good to me.

> 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;

With the goto out_put gone, I'm conflicted whether I find this clearer
here, or ...

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

... even down here:

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

That way bridge doesn't have to be checked twice and all the
modification of *bridge is in the same block.

> 
> 	of_node_put(remote);
> 	return ret;
> }

Either way,

Acked-by: Philipp Zabel <p.zabel@...gutronix.de>

regards
Philipp