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

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Date:	Sun, 01 Dec 2013 12:00:09 -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 11/29/2013 04:46 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.
> 
> Introduced a new struct "of_phandle_iter" to keep the state when
> iterating over the list.
> 
> Signed-off-by: Hiroshi Doyu <hdoyu@...dia.com>
> ---
> v6+++:

Surely that's v9; "+++" is rather unusual.

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

> +void of_phandle_iter_next(struct of_phandle_iter *iter,
> +			  struct of_phandle_args *out_args)
> +{
> +	phandle phandle;
> +	struct device_node *dn;
> +	int i, count = iter->cell_count;
> +
> +	iter->err = -EINVAL;
> +	if (!iter->cells_name && !iter->cell_count)
> +		return;

Wasn't that already checked in _start()?

Why not set err = -EINVAL inside the if, rather than setting it to an
error value here by default, then having to over-write it at the end of
the function?

> +static void __of_phandle_iter_set(struct of_phandle_iter *iter,

This is only used in one place; why not simply inline this into
of_phandle_iter_start()? It would make the code simpler.

> +void of_phandle_iter_start(struct of_phandle_iter *iter,

> +	iter->cells_name = cells_name;
> +	iter->cell_count = cell_count;

Why not pass these values into of_phandle_iter_next() instead? There's
no need to pass them just to _start() so they can be read by _next()
instead.

> diff --git a/include/linux/of.h b/include/linux/of.h

> +/*
> + * keep the state at iterating a list of phandles with variable number
> + * of args
> + */
> +struct of_phandle_iter {
> +	int		err;
> +	const __be32	*cur;		/* current phandle */
> +	const __be32	*end;		/* end of the last phandle */

Can't you detect an error case by e.g. (cur == NULL) and thus avoid
requiring an explicit err field?

Together with removing:

> +	const char	*cells_name;
> +	int		cell_count;

... then you'd only be left with cur/end, so I think you could get away
without a struct at all, but simply "cur" as the iterator variable, plus
"end" as the one temp variable.
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