Re: [PATCH v4 06/13] libfdt: Add max phandle retrieval function

[David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>]

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On Tue, Jul 05, 2016 at 10:26:39AM +0200, Maxime Ripard wrote:
> Add a function to retrieve the highest phandle in a given device tree.
> 
> Signed-off-by: Maxime Ripard <maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
> Reviewed-by: Stefan Agner <stefan-XLVq0VzYD2Y@public.gmane.org>
> Acked-by: Simon Glass <sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
> ---
>  include/libfdt.h    | 13 +++++++++++++
>  lib/libfdt/fdt_ro.c | 26 ++++++++++++++++++++++++++
>  2 files changed, 39 insertions(+)
> 
> diff --git a/include/libfdt.h b/include/libfdt.h
> index fbbe58ceb3f1..4643be5adf39 100644
> --- a/include/libfdt.h
> +++ b/include/libfdt.h
> @@ -283,6 +283,19 @@ int fdt_move(const void *fdt, void *buf, int bufsize);
>   */
>  const char *fdt_string(const void *fdt, int stroffset);
>  
> +/**
> + * fdt_get_max_phandle - retrieves the highest phandle in a tree
> + * @fdt: pointer to the device tree blob
> + *
> + * fdt_get_max_phandle retrieves the highest phandle in the given
> + * device tree
> + *
> + * returns:
> + *      the highest phandle on success
> + *      0, if an error occurred

This will also return 0 if there are no phandles in the entire tree,
which isn't exactly an error.

> + */
> +uint32_t fdt_get_max_phandle(const void *fdt);
> +
>  /**
>   * fdt_num_mem_rsv - retrieve the number of memory reserve map entries
>   * @fdt: pointer to the device tree blob
> diff --git a/lib/libfdt/fdt_ro.c b/lib/libfdt/fdt_ro.c
> index 12214c2dc2b5..503150ef1dc5 100644
> --- a/lib/libfdt/fdt_ro.c
> +++ b/lib/libfdt/fdt_ro.c
> @@ -47,6 +47,32 @@ static int _fdt_string_eq(const void *fdt, int stroffset,
>  	return (strnlen(p, len + 1) == len) && (memcmp(p, s, len) == 0);
>  }
>  
> +uint32_t fdt_get_max_phandle(const void *fdt)
> +{
> +	uint32_t max_phandle = 0;
> +	int offset;
> +
> +	for (offset = fdt_next_node(fdt, -1, NULL);;
> +	     offset = fdt_next_node(fdt, offset, NULL)) {
> +		uint32_t phandle;
> +
> +		if (offset == -FDT_ERR_NOTFOUND)
> +			return max_phandle;
> +
> +		if (offset < 0)
> +			return 0;
> +
> +		phandle = fdt_get_phandle(fdt, offset);
> +		if (phandle == (uint32_t)-1)
> +			return 0;

It might be worth pointing out that *any* -1 phandle in the tree
counts as an error.  Since -1 phandles are sometimes used as a
placeholder, ignoring them might be a better option.

> +		if (phandle > max_phandle)
> +			max_phandle = phandle;
> +	}
> +
> +	return 0;
> +}
> +
>  int fdt_get_mem_rsv(const void *fdt, int n, uint64_t *address, uint64_t *size)
>  {
>  	FDT_CHECK_HEADER(fdt);

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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