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>

1 files changed, 15 insertions, 0 deletions

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);