xtensa: implement ndelay

Proper ndelay implementation allows for faster IO rate with drivers that
use ndelay to access their device registers, as otherwise ndelay is
emulated with udelay.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/arch/xtensa/include/asm/delay.h b/arch/xtensa/include/asm/delay.h
index 69ba4629bed0..24304b39a5c7 100644
--- a/arch/xtensa/include/asm/delay.h
+++ b/arch/xtensa/include/asm/delay.h
@@ -29,8 +29,10 @@ static inline void __delay(unsigned long loops)
 
 /* Undefined function to get compile-time error */
 void __bad_udelay(void);
+void __bad_ndelay(void);
 
 #define __MAX_UDELAY 30000
+#define __MAX_NDELAY 30000
 
 static inline void __udelay(unsigned long usecs)
 {
@@ -50,4 +52,24 @@ static inline void udelay(unsigned long usec)
                 __udelay(usec);
 }
 
+static inline void __ndelay(unsigned long nsec)
+{
+        /*
+         * Inner shift makes sure multiplication doesn't overflow
+         * for legitimate nsec values
+         */
+        unsigned long cycles = (nsec * (ccount_freq >> 15)) >> 15;
+        __delay(cycles);
+}
+
+#define ndelay(n) ndelay(n)
+
+static inline void ndelay(unsigned long nsec)
+{
+        if (__builtin_constant_p(nsec) && nsec >= __MAX_NDELAY)
+                __bad_ndelay();
+        else
+                __ndelay(nsec);
+}
+
 #endif