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libfdt: Add phandle generation helper

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The new fdt_generate_phandle() function can be used to generate a new,
unused phandle given a specific device tree blob. The implementation is
somewhat naive in that it simply walks the entire device tree to find
the highest phandle value and then returns a phandle value one higher
than that. A more clever implementation might try to find holes in the
current set of phandle values and fill them. But this implementation is
relatively simple and works reliably.

Also add a test that validates that phandles generated by this new API
are indeed unique.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Message-Id: <20190326153302.17109-3-thierry.reding@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Thierry Reding 2019-03-26 16:33:02 +01:00 • committed by David Gibson
parent 7dfb61ba96
commit 730875016a
8 changed files with 99 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

18
libfdt/fdt_ro.c
View file

@ -184,6 +184,24 @@ uint32_t fdt_get_max_phandle(const void *fdt)
return phandle;
}
int fdt_generate_phandle(const void *fdt, uint32_t *phandle)
{
uint32_t max;
int err;
err = fdt_find_max_phandle(fdt, &max);
if (err < 0)
return err;
if (max == FDT_MAX_PHANDLE)
return -FDT_ERR_NOPHANDLES;
if (phandle)
*phandle = max + 1;
return 0;
}
static const struct fdt_reserve_entry *fdt_mem_rsv(const void *fdt, int n)
{
int offset = n * sizeof(struct fdt_reserve_entry);

19
libfdt/libfdt.h
View file

@ -140,6 +140,10 @@
#define FDT_ERR_MAX 17
/* constants */
#define FDT_MAX_PHANDLE 0xfffffffe
/* Valid values for phandles range from 1 to 2^32-2. */
/**********************************************************************/
/* Low-level functions (you probably don't need these) */
/**********************************************************************/
@ -416,6 +420,21 @@ int fdt_find_max_phandle(const void *fdt, uint32_t *phandle);
*/
uint32_t fdt_get_max_phandle(const void *fdt);
/**
* fdt_generate_phandle - return a new, unused phandle for a device tree blob
* @fdt: pointer to the device tree blob
* @phandle: return location for the new phandle
*
* Walks the device tree blob and looks for the highest phandle value. On
* success, the new, unused phandle value (one higher than the previously
* highest phandle value in the device tree blob) will be returned in the
* @phandle parameter.
*
* Returns:
* 0 on success or a negative error-code on failure
*/
int fdt_generate_phandle(const void *fdt, uint32_t *phandle);
/**
* fdt_num_mem_rsv - retrieve the number of memory reserve map entries
* @fdt: pointer to the device tree blob

1
libfdt/version.lds
View file

@ -68,6 +68,7 @@ LIBFDT_1.2 {
fdt_get_string;
fdt_find_max_phandle;
fdt_get_max_phandle;
fdt_generate_phandle;
fdt_check_full;
fdt_setprop_placeholder;
fdt_property_placeholder;