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

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 04.03.24 10:37, Sascha Hauer wrote:
> 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

Ouch. Thanks for fixing!

> 
> Sascha
> 

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