Re: [PATCH 2/4] of: fdt: implement fdt_machine_is_compatible

[Sascha Hauer <s.hauer@pengutronix.de>]

On Fri, Mar 01, 2024 at 02:04:43PM +0100, Ahmad Fatoum wrote:
> When finding compatible bootloader spec files, barebox will unflatten
> each DTB in turn, allocating objects for each property and node, only to
> compare a single property and then free all the allocations again.
> 
> Given that this operation is repeated for every device tree until a
> match is found, it's a good idea to be able to compare machine
> (top-level) compatibles without having to unflatten the whole FDT.
> 
> Implemnt fdt_machine_is_compatible() that does just that. This
> intentionally opencodes the device tree iteration as to minimize
> code and runtime size. Using libfdt without LTO would be slower
> and bigger.
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
>  drivers/of/fdt.c | 95 ++++++++++++++++++++++++++++++++++++++++++++++++
>  include/of.h     |  3 ++
>  2 files changed, 98 insertions(+)
> 
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index 676b8a5535bf..aa3d2e967acd 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -668,3 +668,98 @@ void fdt_print_reserve_map(const void *__fdt)
>  			return;
>  	}
>  }
> +
> +static int fdt_string_is_compatible(const char *haystack, int haystack_len,
> +				    const char *needle, int needle_len)
> +{
> +	const char *p;
> +	int index = 0;
> +
> +	while (haystack_len >= needle_len) {
> +		if (memcmp(needle, haystack, needle_len + 1) == 0)
> +			return OF_DEVICE_COMPATIBLE_MAX_SCORE - (index << 2);
> +
> +		p = memchr(haystack, '\0', haystack_len);
> +		if (!p)
> +			return 0;
> +		haystack_len -= (p - haystack) + 1;
> +		haystack = p + 1;
> +		index++;
> +	}
> +
> +	return 0;
> +}
> +
> +bool fdt_machine_is_compatible(const struct fdt_header *fdt, size_t fdt_size, const char *compat)
> +{
> +	uint32_t tag;
> +	const struct fdt_property *fdt_prop;
> +	const char *name;
> +	uint32_t dt_struct;
> +	const struct fdt_node_header *fnh;
> +	const void *dt_strings;
> +	struct fdt_header f;
> +	int ret, len;
> +	int expect = FDT_BEGIN_NODE;
> +	int compat_len = strlen(compat);
> +
> +	ret = fdt_parse_header(fdt, fdt_size, &f);
> +	if (ret < 0)
> +		return ERR_PTR(ret);

return false here

Sascha

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