Re: [PATCHv6+ 01/13] of: introduce of_property_for_earch_phandle_with_args()

[Grant Likely]

On Wed, 11 Dec 2013 14:33:38 +0100, Hiroshi Doyu <hdoyu@xxxxxxxxxx> wrote:
> Hi Grant,
> 
> Grant Likely <grant.likely@xxxxxxxxxx> wrote @ Wed, 11 Dec 2013 14:28:45 +0100:
> 
> > On Thu, 21 Nov 2013 11:57:00 -0700, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote:
> > > On 11/21/2013 10:17 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.
> > > > 
> > > > Signed-off-by: Hiroshi Doyu <hdoyu@xxxxxxxxxx>
> > > > ---
> > > > v6+:
> > > > Use the description, which Grant Likely proposed, to be full enough
> > > > that a future reader can figure out why a patch was written.
> > > >   http://lists.linuxfoundation.org/pipermail/iommu/2013-November/007062.html
> ...
> 
> > That's right, I forgot I said that. Yes please fix the implementation.
> 
> Here's the latest. I'll include this with the next v7 series.
> 
> Can I get your Acked-by with this?
> 
> --8<----
> 
> From 8f7c0404aa68f0e8dbe0babc240590f6528ecc1f Mon Sep 17 00:00:00 2001
> From: Hiroshi Doyu <hdoyu@xxxxxxxxxx>
> Date: Fri, 15 Nov 2013 10:52:53 +0200
> Subject: [PATCH] of: introduce of_property_for_each_phandle_with_args()
> 
> 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.
> 
> Signed-off-by: Hiroshi Doyu <hdoyu@xxxxxxxxxx>
> Cc: Rob Herring <robherring2@xxxxxxxxx>
> ---
> v7:
> Fixed some minors pointed by Rob and Stephen.
> 
> v6++++:
> Iterate without intrducing a new struct.
> 
> v6+++:
> Introduced a new struct "of_phandle_iter" to keep the state when
> iterating over the list.
> 
> v6++:
> Optimized to avoid O(n^2), suggested by Stephen Warren.
> http://lists.linuxfoundation.org/pipermail/iommu/2013-November/007066.html
> 
> I didn't introduce any struct to hold params and state here.
> 
> v6+:
> Use the description, which Grant Likely proposed, to be full enough
> that a future reader can figure out why a patch was written.
> 
> v5:
> New patch for v5.
> 
> Signed-off-by: Hiroshi Doyu <hdoyu@xxxxxxxxxx>
> ---
>  drivers/of/base.c  | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/of.h | 32 ++++++++++++++++++++++++++++++++
>  2 files changed, 78 insertions(+)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index f807d0e..cd4ab05 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -1201,6 +1201,52 @@ void of_print_phandle_args(const char *msg, const struct of_phandle_args *args)
>  	printk("\n");
>  }
>  
> +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)

Having to pass in cells_name, cell_count, cur and end each time seems a
little odd. Can a state structure be used instead?

struct of_phandle_iter_state {
	const char *cells_name;
	int cells_count;
	const __be32 *cur;
	const __be32 *end;
	struct of_phandle_args out_args;
}

Make the caller provide one of those and fill it in with the init
function.

> +{
> +	struct device_node *dn;
> +	int i;
> +
> +	if (!cells_name && !cell_count)
> +		return NULL;
> +
> +	if (!cur || (cur >= end))
> +		return NULL;
> +
> +	dn = of_find_node_by_phandle(be32_to_cpup(cur++));
> +	if (!dn)
> +		return NULL;
> +
> +	if (cells_name)
> +		if (of_property_read_u32(dn, cells_name, &cell_count))
> +			return NULL;
> +
> +	out_args->np = dn;
> +	out_args->args_count = cell_count;
> +	for (i = 0; i < cell_count; i++)
> +		out_args->args[i] = be32_to_cpup(cur++);
> +
> +	return cur;
> +}
> +EXPORT_SYMBOL_GPL(of_phandle_iter_next);
> +
> +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);
> +	*end = cur;
> +	if (bytes)
> +		*end += bytes / sizeof(*cur);
> +
> +	return cur;
> +}
> +EXPORT_SYMBOL_GPL(of_phandle_iter_init);
> +
>  static int __of_parse_phandle_with_args(const struct device_node *np,
>  					const char *list_name,
>  					const char *cells_name,
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 276c546..4345582 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -303,6 +303,14 @@ extern int of_parse_phandle_with_fixed_args(const struct device_node *np,
>  extern int of_count_phandle_with_args(const struct device_node *np,
>  	const char *list_name, const char *cells_name);
>  
> +extern const __be32 *of_phandle_iter_init(const struct device_node *np,
> +					  const char *list_name,
> +					  const __be32 **end);
> +extern 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);
> +
>  extern void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align));
>  extern int of_alias_get_id(struct device_node *np, const char *stem);
>  
> @@ -527,6 +535,22 @@ static inline int of_count_phandle_with_args(struct device_node *np,
>  	return -ENOSYS;
>  }
>  
> +static inline const __be32 *of_phandle_iter_init(const struct device_node *np,
> +						 const char *list_name,
> +						 const __be32 **end)
> +{
> +	return NULL;
> +}
> +
> +static inline 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);
> +{
> +	return NULL;
> +}
> +
>  static inline int of_alias_get_id(struct device_node *np, const char *stem)
>  {
>  	return -ENOSYS;
> @@ -613,6 +637,14 @@ static inline int of_property_read_u32(const struct device_node *np,
>  		s;						\
>  		s = of_prop_next_string(prop, s))
>  
> +#define of_property_for_each_phandle_with_args(node, list_name, cells_name, \
> +					       cell_count, out_args, cur, end) \
> +	for (cur = of_phandle_iter_init(node, list_name, &end),		\
> +		     cur = of_phandle_iter_next(cells_name, cell_count, \
> +						cur, end, &out_args);	\

The above construct is a little odd. Why wouldn't the initializer
provide the first element (or NULL if empty) right at the start. That in
combination with the suggestion I made above would change the macro to
be:

#define of_property_for_each_phandle_with_args(node, list_name, cells_name, \
					       cell_count, &iter_state) \
	for (cur = of_phandle_iter_init(node, list_name, cells_name, \
					cells_count, &iter_state); \
	    cur; cur = of_phandle_iter_next(&iter_state)) \

Simpler, right? It also means whatever the user passed in for
cells_name, cell_count won't get evaluated every time through the loop.

g.

> +	     cur;							\
> +	     cur = of_phandle_iter_next(cells_name, cell_count, cur, end, &out_args))
> +
>  #if defined(CONFIG_PROC_FS) && defined(CONFIG_PROC_DEVICETREE)
>  extern void proc_device_tree_add_node(struct device_node *, struct proc_dir_entry *);
>  extern void proc_device_tree_add_prop(struct proc_dir_entry *pde, struct property *prop);
> -- 
> 1.8.1.5

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