Re: [PATCH 1/3] of: Support parsing phandle argument lists through a nexus node

[Pantelis Antoniou]

Hi Stephen,

> On Nov 24, 2016, at 12:25 , Stephen Boyd <stephen.boyd@xxxxxxxxxx> wrote:
> 
> Platforms like 96boards have a standardized connector/expansion
> slot that exposes signals like GPIOs to expansion boards in an
> SoC agnostic way. We'd like the DT overlays for the expansion
> boards to be written once without knowledge of the SoC on the
> other side of the connector. This avoids the unscalable
> combinatorial explosion of a different DT overlay for each
> expansion board and SoC pair.
> 
> We need a way to describe the GPIOs routed through the connector
> in an SoC agnostic way. Let's introduce nexus property parsing
> into the OF core to do this. This is largely based on the
> interrupt nexus support we already have. This allows us to remap
> a phandle list in a consumer node (e.g. reset-gpios) through a
> connector in a generic way (e.g. via gpio-map). Do this in a
> generic routine so that we can remap any sort of variable length
> phandle list.
> 
> Taking GPIOs as an example, the connector would be a GPIO nexus,
> supporting the remapping of a GPIO specifier space to multiple
> GPIO providers on the SoC. DT would look as shown below, where
> 'soc_gpio1' and 'soc_gpio2' are inside the SoC, 'connector' is an
> expansion port where boards can be plugged in, and
> 'expansion_device' is a device on the expansion board.
> 
> 	soc {
> 		soc_gpio1: gpio-controller1 {
> 			#gpio-cells = <2>;
> 		};
> 
> 		soc_gpio2: gpio-controller2 {
> 			#gpio-cells = <2>;
> 		};
> 	};
> 
> 	connector: connector {
> 		#gpio-cells = <2>;
> 		gpio-map = <0 GPIO_ACTIVE_LOW &soc_gpio1 1 GPIO_ACTIVE_LOW>,
> 			   <1 GPIO_ACTIVE_LOW &soc_gpio2 4 GPIO_ACTIVE_LOW>,
> 			   <2 GPIO_ACTIVE_LOW &soc_gpio1 3 GPIO_ACTIVE_LOW>,
> 			   <3 GPIO_ACTIVE_LOW &soc_gpio2 2 GPIO_ACTIVE_LOW>;
> 		gpio-map-mask = <0xf 0x1>;
> 	};
> 
> 	expansion_device {
> 		reset-gpios = <&connector 2 GPIO_ACTIVE_LOW>;
> 	};
> 
> The GPIO core would use of_parse_phandle_with_args_map() instead
> of of_parse_phandle_with_args() and arrive at the same type of
> result, a phandle and argument list. The difference is that the
> phandle and arguments will be remapped through the nexus node to
> the underlying SoC GPIO controller node. In the example above,
> we would remap 'reset-gpios' from <&connector 2 GPIO_ACTIVE_LOW>
> to <&soc_gpio1 3 GPIO_ACTIVE_LOW>.
> 

Very good. My only point would be to elaborate a little bit on the
documentation part about how there might be different #list-cells values
pointed at, and how the lookup is performed in steps.

> Cc: Pantelis Antoniou <pantelis.antoniou@xxxxxxxxxxxx>
> Cc: Linus Walleij <linus.walleij@xxxxxxxxxx>
> Cc: Mark Brown <broonie@xxxxxxxxxx>
> Signed-off-by: Stephen Boyd <stephen.boyd@xxxxxxxxxx>
> ---
> drivers/of/base.c  | 146 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/of.h |  14 +++++
> 2 files changed, 160 insertions(+)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index d687e6de24a0..693b73f33675 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -1772,6 +1772,152 @@ int of_parse_phandle_with_args(const struct device_node *np, const char *list_na
> EXPORT_SYMBOL(of_parse_phandle_with_args);
> 
> /**
> + * of_parse_phandle_with_args_map() - Find a node pointed by phandle in a list and remap it
> + * @np:		pointer to a device tree node containing a list
> + * @list_name:	property name that contains a list
> + * @cells_name:	property name that specifies phandles' arguments count
> + * @index:	index of a phandle to parse out
> + * @out_args:	optional pointer to output arguments structure (will be filled)
> + *
> + * This function is useful to parse lists of phandles and their arguments.
> + * Returns 0 on success and fills out_args, on error returns appropriate
> + * errno value.
> + *
> + * Caller is responsible to call of_node_put() on the returned out_args->np
> + * pointer.
> + *
> + * Example:
> + *
> + * phandle1: node1 {
> + *	#list-cells = <2>;
> + * }
> + *
> + * phandle2: node2 {
> + *	#list-cells = <1>;
> + * }
> + *
> + * phandle3: node3 {
> + * 	#list-cells = <1>;
> + * 	list-map = <0 &phandle2 3>,
> + * 		   <1 &phandle2 2>,
> + * 		   <2 &phandle1 5 1>;
> + *	list-map-mask = <0x3>;
> + * };
> + *
> + * node4 {
> + *	list = <&phandle1 1 2 &phandle3 0>;
> + * }
> + *
> + * To get a device_node of the `node2' node you may call this:
> + * of_parse_phandle_with_args(node4, "list", "#list-cells", "list-map",
> + * 			      "list-map-mask", 1, &args);
> + */
> +int of_parse_phandle_with_args_map(const struct device_node *np,
> +				   const char *list_name,
> +				   const char *cells_name,
> +				   const char *map_name,
> +				   const char *mask_name,
> +				   int index, struct of_phandle_args *out_args)
> +{
> +	struct device_node *cur, *new = NULL;
> +	const __be32 *map, *mask, *tmp;
> +	const __be32 dummy_mask[] = { [0 ... MAX_PHANDLE_ARGS] = ~0 };
> +	__be32 initial_match_array[MAX_PHANDLE_ARGS];
> +	const __be32 *match_array = initial_match_array;
> +	int i, ret, map_len, match;
> +	u32 list_size, new_size;
> +
> +	if (index < 0)
> +		return -EINVAL;
> +
> +	ret = __of_parse_phandle_with_args(np, list_name, cells_name, 0, index,
> +					   out_args);
> +	if (ret)
> +		return ret;
> +
> +	/* Get the #<list>-cells property */
> +	cur = out_args->np;
> +	ret = of_property_read_u32(cur, cells_name, &list_size);
> +	if (ret < 0)
> +		goto fail;
> +
> +	/* Precalculate the match array - this simplifies match loop */
> +	for (i = 0; i < list_size; i++)
> +		initial_match_array[i] = cpu_to_be32(out_args->args[i]);
> +
> +	while (cur) {
> +		/* Get the <list>-map property */
> +		map = of_get_property(cur, map_name, &map_len);
> +		if (!map)
> +			return 0;
> +		map_len /= sizeof(u32);
> +
> +		/* Get the <list>-map-mask property (optional) */
> +		mask = of_get_property(cur, mask_name, NULL);
> +		if (!mask)
> +			mask = dummy_mask;
> +
> +		/* Iterate through <list>-map property */
> +		match = 0;
> +		while (map_len > (list_size + 1) && !match) {
> +			/* Compare specifiers */
> +			match = 1;
> +			for (i = 0; i < list_size; i++, map_len--)
> +				match &= !((match_array[i] ^ *map++) & mask[i]);
> +
> +			of_node_put(new);
> +			new = of_find_node_by_phandle(be32_to_cpup(map));
> +			map++;
> +			map_len--;
> +
> +			/* Check if not found */
> +			if (!new)
> +				goto fail;
> +
> +			if (!of_device_is_available(new))
> +				match = 0;
> +
> +			tmp = of_get_property(new, cells_name, NULL);
> +			if (!tmp)
> +				goto fail;
> +
> +			new_size = be32_to_cpu(*tmp);
> +
> +			/* Check for malformed properties */
> +			if (WARN_ON(new_size > MAX_PHANDLE_ARGS))
> +				goto fail;
> +			if (map_len < new_size)
> +				goto fail;
> +
> +			/* Move forward by new node's #<list>-cells amount */
> +			map += new_size;
> +			map_len -= new_size;
> +		}
> +		if (!match)
> +			goto fail;
> +
> +		/*
> +		 * Successfully parsed a <list>-map translation; copy new
> +		 * specifier into the out_args structure.
> +		 */
> +		match_array = map - new_size;
> +		for (i = 0; i < new_size; i++)
> +			out_args->args[i] = be32_to_cpup(map - new_size + i);
> +		out_args->args_count = list_size = new_size;
> +		/* Iterate again with new provider */
> +		out_args->np = new;
> +		of_node_put(cur);
> +		cur = new;
> +	}
> +fail:
> +	of_node_put(cur);
> +	of_node_put(new);
> +
> +	return -EINVAL;
> +}
> +EXPORT_SYMBOL(of_parse_phandle_with_args_map);
> +
> +/**
>  * of_parse_phandle_with_fixed_args() - Find a node pointed by phandle in a list
>  * @np:		pointer to a device tree node containing a list
>  * @list_name:	property name that contains a list
> diff --git a/include/linux/of.h b/include/linux/of.h
> index d3a9c2e69001..65ff306403a2 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -344,6 +344,9 @@ extern struct device_node *of_parse_phandle(const struct device_node *np,
> extern int of_parse_phandle_with_args(const struct device_node *np,
> 	const char *list_name, const char *cells_name, int index,
> 	struct of_phandle_args *out_args);
> +extern int of_parse_phandle_with_args_map(const struct device_node *np,
> +	const char *list_name, const char *cells_name, const char *map_name,
> +	const char *mask_name, int index, struct of_phandle_args *out_args);
> extern int of_parse_phandle_with_fixed_args(const struct device_node *np,
> 	const char *list_name, int cells_count, int index,
> 	struct of_phandle_args *out_args);
> @@ -738,6 +741,17 @@ static inline int of_parse_phandle_with_args(const struct device_node *np,
> 	return -ENOSYS;
> }
> 
> +static inline int of_parse_phandle_with_args_map(const struct device_node *np,
> +						 const char *list_name,
> +						 const char *cells_name,
> +						 const char *map_name,
> +						 const char *mask_name,
> +						 int index,
> +						 struct of_phandle_args *out_args)
> +{
> +	return -ENOSYS;
> +}
> +
> static inline int of_parse_phandle_with_fixed_args(const struct device_node *np,
> 	const char *list_name, int cells_count, int index,
> 	struct of_phandle_args *out_args)
> -- 
> 2.10.0.297.gf6727b0
>