[PATCH 09/27] libfdt: Add phandle generation helper

[Sebastian Huber]

From: Thierry Reding <treding at nvidia.com>

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 at nvidia.com>
Message-Id: <20190326153302.17109-3-thierry.reding at gmail.com>
Signed-off-by: David Gibson <david at gibson.dropbear.id.au>
---
 cpukit/dtc/libfdt/fdt_ro.c | 18 ++++++++++++++++++
 cpukit/include/libfdt.h    | 19 +++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/cpukit/dtc/libfdt/fdt_ro.c b/cpukit/dtc/libfdt/fdt_ro.c
index 1d0335ee71..817ac39099 100644
--- a/cpukit/dtc/libfdt/fdt_ro.c
+++ b/cpukit/dtc/libfdt/fdt_ro.c
@@ -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);
diff --git a/cpukit/include/libfdt.h b/cpukit/include/libfdt.h
index e1498c3c21..39ff6d5d25 100644
--- a/cpukit/include/libfdt.h
+++ b/cpukit/include/libfdt.h
@@ -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
-- 
2.16.4