CRIS v32: Add precise delay loops for ETRAX FS and ARTPEC-3.

Implements cris_delay10ns.

arch/cris/arch-v32/lib/delay.c

+/*
+ * Precise Delay Loops for ETRAX FS
+ *
+ * Copyright (C) 2006 Axis Communications AB.
+ *
+ */
+
+#include <hwregs/reg_map.h>
+#include <hwregs/reg_rdwr.h>
+#include <hwregs/timer_defs.h>
+#include <linux/types.h>
+#include <linux/delay.h>
+#include <linux/module.h>
+
+/*
+ * On ETRAX FS, we can check the free-running read-only 100MHz timer
+ * getting 32-bit 10ns precision, theoretically good for 42.94967295
+ * seconds.  Unsigned arithmetic and careful expression handles
+ * wrapping.
+ */
+
+void cris_delay10ns(u32 n10ns)
+{
+	u32 t0 = REG_RD(timer, regi_timer0, r_time);
+	while (REG_RD(timer, regi_timer0, r_time) - t0 < n10ns)
+		;
+}
+EXPORT_SYMBOL(cris_delay10ns);