linux-kernel - Re: [RFC][PATCHv6+++ 01/13] of: introduce of_property_for_earch_phandle_with

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Date:	Tue, 03 Dec 2013 13:14:18 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Hiroshi Doyu <hdoyu@...dia.com>
CC:	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"thierry.reding@...il.com" <thierry.reding@...il.com>,
	"robherring2@...il.com" <robherring2@...il.com>,
	"joro@...tes.org" <joro@...tes.org>,
	Stephen Warren <swarren@...dia.com>,
	"will.deacon@....com" <will.deacon@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCHv6+++ 01/13] of: introduce of_property_for_earch_phandle_with_args()

On 12/02/2013 04:02 AM, Hiroshi Doyu wrote:
...
> Iterating over a property containing a list of phandles with arguments
> is a common operation for device drivers. This patch adds a new
> of_property_for_each_phandle_with_args() macro to make the iteration
> simpler.

> diff --git a/drivers/of/base.c b/drivers/of/base.c

> +const __be32 *of_phandle_iter_init(const struct device_node *np,
> +				   const char *list_name,
> +				   const __be32 **end)
> +{
> +	size_t bytes;
> +	const __be32 *cur;
> +
> +	cur = of_get_property(np, list_name, &bytes);
> +	if (bytes)
> +		*end = cur + bytes / sizeof(*cur);
> +
> +	return cur;
> +}

"bytes" doesn't seem like the correct thing to check in that if
statement. The property might exist but be zero length. Perhaps if (cur)
would be better, or just initializing *end in all cases (the value won't
be used if (!cur), so setting *end to a bogus value in that case won't
matter).

> +const __be32 *of_phandle_iter_next(const char *cells_name, int cell_count,
> +				   const __be32 *cur, const __be32 *end,
> +				   struct of_phandle_args *out_args)
...
> +	if (!cur)
> +		return NULL;
> +
> +	if (end - cur <= 0)
> +		return NULL;

Related, don't you want if (cur >= end) there; just compare the pointers
directly rather than explicitly calculating and testing the difference?
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