fdt: Add function to read a clock rate from fdt

This reads the frequency of a named clock from the fdt.

BUG=chromium-os:23496
TEST=build and boot on Seaboard, T33, Kaen
Change-Id: Ib35bf7ef749f51862644218b1015057ca4e25203
Reviewed-on: https://gerrit.chromium.org/gerrit/12243
Reviewed-by: Che-Liang Chiou <clchiou@chromium.org>
Commit-Ready: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>

2 files changed, 30 insertions, 0 deletions

diff --git a/common/fdt_decode.c b/common/fdt_decode.c
index 96807c47c9..3d956c3c16 100644
--- a/common/fdt_decode.c
+++ b/common/fdt_decode.c
@@ -718,3 +718,18 @@ int fdt_decode_region(const void *blob, int node,
 	debug("%s: size=%zx\n", __func__, *size);
 	return 0;
 }
+
+int fdt_decode_clock_rate(const void *blob, const char *clock_name,
+			  ulong default_rate)
+{
+	int node;
+
+	node = fdt_node_offset_by_compatible(blob, 0, "board-clocks");
+	if (node >= 0) {
+		node = lookup_phandle(blob, node, clock_name);
+		if (node >= 0)
+			return get_int(blob, node, "clock-frequency",
+				       default_rate);
+	}
+	return default_rate;
+}
diff --git a/include/fdt_decode.h b/include/fdt_decode.h
index 6087c21861..68d31653b5 100644
--- a/include/fdt_decode.h
+++ b/include/fdt_decode.h
@@ -614,3 +614,18 @@ int fdt_decode_nand(const void *blob, int node, struct fdt_nand *config);
  */
 int fdt_decode_region(const void *blob, int node,
 		const char *prop_name, void **ptrp, size_t *size);
+
+/**
+ * Look up the required rate of a particular clock in the FDT.
+ *
+ * These are expected to be in a board-clocks compatible node, with a
+ * property pointing to the phandle of each clock. The clock-frequency
+ * property in that phandle is returned.
+ *
+ * @param blob		FDT blob
+ * @param clock_name	Name of clock to look up (must name a phandle)
+ * @param default_rate	Default clock rate to return if property not found
+ * @return clock rate as found in FDT, or default_rate if not found
+ */
+int fdt_decode_clock_rate(const void *blob, const char *clock_name,
+			  ulong default_rate);