clkdev: add possibility to get a clock based on the device name

This adds clk_get_sys to get a clock without the associated struct
device.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

include/linux/clk.h

@@ -125,4 +125,21 @@ int clk_set_parent(struct clk *clk, struct clk *parent);
  */
 struct clk *clk_get_parent(struct clk *clk);
 
+/**
+ * clk_get_sys - get a clock based upon the device name
+ * @dev_id: device name
+ * @con_id: connection ID
+ *
+ * Returns a struct clk corresponding to the clock producer, or
+ * valid IS_ERR() condition containing errno.  The implementation
+ * uses @dev_id and @con_id to determine the clock consumer, and
+ * thereby the clock producer. In contrast to clk_get() this function
+ * takes the device name instead of the device itself for identification.
+ *
+ * Drivers must assume that the clock source is not enabled.
+ *
+ * clk_get_sys should not be called from within interrupt context.
+ */
+struct clk *clk_get_sys(const char *dev_id, const char *con_id);
+
 #endif