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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: <20190320151003.28941-1-thierry.reding@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Thierry Reding
2019-03-20 16:10:03 +01:00
committed by David Gibson
parent 4762ad051e
commit 54ea41c224
9 changed files with 114 additions and 3 deletions
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19
libfdt/libfdt.h
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@@ -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) */
/**********************************************************************/
@@ -376,6 +380,21 @@ const char *fdt_string(const void *fdt, int stroffset);
*/
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