
diff --git a/include/asm-arm/div64.h b/include/asm-arm/div64.h
index 3682616..b89108f 100644
--- a/include/asm-arm/div64.h
+++ b/include/asm-arm/div64.h
@@ -27,7 +27,7 @@
 #define __xh "r1"
 #endif
 
-#define do_div(n,base)						\
+#define __do_div_asm(n, base)					\
 ({								\
 	register unsigned int __base      asm("r4") = base;	\
 	register unsigned long long __n   asm("r0") = n;	\
@@ -45,4 +45,183 @@
 	__rem;							\
 })
 
+
+#if __GNUC__ < 4
+
+/*
+ * gcc versions earlier than 4.0 are simply too problematic for the
+ * optimized implementation below. First there is gcc PR 15089 that
+ * tend to trig on more complex constructs, spurious .global __udivsi3
+ * are inserted even if none of those symbols are referenced in the
+ * generated code, and those gcc versions are not able to do constant
+ * propagation on long long values anyway.
+ */
+#define do_div(n, base) __do_div_asm(n, base)
+
+#elif __GNUC__ >= 4
+
+#include <asm/bug.h>
+
+/*
+ * If the divisor happens to be constant, we determine the appropriate
+ * inverse at compile time to turn the division into a few inline
+ * multiplications instead which is much faster. And yet only if compiling
+ * for ARMv4 or higher (we need umull/umlal) and if the gcc version is
+ * sufficiently recent to perform proper long long constant propagation.
+ * (It is unfortunate that gcc doesn't perform all this internally.)
+ */
+#define do_div(n, base)							\
+({									\
+	unsigned int __r, __b = (base);					\
+	if (!__builtin_constant_p(__b) || __b == 0 ||			\
+	    (__LINUX_ARM_ARCH__ < 4 && (__b & (__b - 1)) != 0)) {	\
+		/* non-constant divisor (or zero): slow path */		\
+		__r = __do_div_asm(n, __b);				\
+	} else if ((__b & (__b - 1)) == 0) {				\
+		/* Trivial: __b is constant and a power of 2 */		\
+		/* gcc does the right thing with this code.  */		\
+		__r = n;						\
+		__r &= (__b - 1);					\
+		n /= __b;						\
+	} else {							\
+		/* Multiply by inverse of __b: n/b = n*(p/b)/p       */	\
+		/* We rely on the fact that most of this code gets   */	\
+		/* optimized away at compile time due to constant    */	\
+		/* propagation and only a couple inline assembly     */	\
+		/* instructions should remain. Better avoid any      */	\
+		/* code construct that might prevent that.           */	\
+		unsigned long long __res, __x, __t, __m, __n = n;	\
+		unsigned int __c, __p, __z = 0;				\
+		/* preserve low part of n for reminder computation */	\
+		__r = __n;						\
+		/* determine number of bits to represent __b */		\
+		__p = 1 << __div64_fls(__b);				\
+		/* compute __m = ((__p << 64) + __b - 1) / __b */	\
+		__m = (~0ULL / __b) * __p;				\
+		__m += (((~0ULL % __b + 1) * __p) + __b - 1) / __b;	\
+		/* compute __res = __m*(~0ULL/__b*__b-1)/(__p << 64) */	\
+		__x = ~0ULL / __b * __b - 1;				\
+		__res = (__m & 0xffffffff) * (__x & 0xffffffff);	\
+		__res >>= 32;						\
+		__res += (__m & 0xffffffff) * (__x >> 32);		\
+		__t = __res;						\
+		__res += (__x & 0xffffffff) * (__m >> 32);		\
+		__t = (__res < __t) ? (1ULL << 32) : 0;			\
+		__res = (__res >> 32) + __t;				\
+		__res += (__m >> 32) * (__x >> 32);			\
+		__res /= __p;						\
+		/* Now sanitize and optimize what we've got. */		\
+		if (~0ULL % (__b / (__b & -__b)) == 0) {		\
+			/* those cases can be simplified with: */	\
+			__n /= (__b & -__b);				\
+			__m = ~0ULL / (__b / (__b & -__b));		\
+			__p = 1;					\
+			__c = 1;					\
+		} else if (__res != __x / __b) {			\
+			/* We can't get away without a correction    */	\
+			/* to compensate for bit truncation errors.  */	\
+			/* To avoid it we'd need an additional bit   */	\
+			/* to represent __m which would overflow it. */	\
+			/* Instead we do m=p/b and n/b=(n*m+m)/p.    */	\
+			__c = 1;					\
+			/* Compute __m = (__p << 64) / __b */		\
+			__m = (~0ULL / __b) * __p;			\
+			__m += ((~0ULL % __b + 1) * __p) / __b;		\
+		} else {						\
+			/* Reduce __m/__p, and try to clear bit 31   */	\
+			/* of __m when possible otherwise that'll    */	\
+			/* need extra overflow handling later.       */	\
+			unsigned int __bits = -(__m & -__m);		\
+			__bits |= __m >> 32;				\
+			__bits = (~__bits) << 1;			\
+			/* If __bits == 0 then setting bit 31 is     */	\
+			/* unavoidable.  Simply apply the maximum    */	\
+			/* possible reduction in that case.          */	\
+			/* Otherwise the MSB of __bits indicates the */	\
+			/* best reduction we should apply.           */	\
+			if (!__bits) {					\
+				__p /= (__m & -__m);			\
+				__m /= (__m & -__m);			\
+			} else {					\
+				__p >>= __div64_fls(__bits);		\
+				__m >>= __div64_fls(__bits);		\
+			}						\
+			/* No correction needed. */			\
+			__c = 0;					\
+		}							\
+		/* Now we have a combination of 2 conditions:        */	\
+		/* 1) whether or not we need a correction (__c), and */	\
+		/* 2) whether or not there might be an overflow in   */	\
+		/*    the cross product (__m & ((1<<63) | (1<<31)))  */	\
+		/* Select the best insn combination to perform the   */	\
+		/* actual __m * __n / (__p << 64) operation.         */	\
+		if (!__c) {						\
+			asm (	"umull	%Q0, %R0, %1, %Q2\n\t"		\
+				"mov	%Q0, #0"			\
+				: "=&r" (__res)				\
+				: "r" (__m), "r" (__n)			\
+				: "cc" );				\
+		} else if (!(__m & ((1ULL << 63) | (1ULL << 31)))) {	\
+			__res = __m;					\
+			asm (	"umlal	%Q0, %R0, %Q1, %Q2\n\t"		\
+				"mov	%Q0, #0"			\
+				: "+r" (__res)				\
+				: "r" (__m), "r" (__n)			\
+				: "cc" );				\
+		} else {						\
+			asm (	"umull	%Q0, %R0, %Q1, %Q2\n\t"		\
+				"cmn	%Q0, %Q1\n\t"			\
+				"adcs	%R0, %R0, %R1\n\t"		\
+				"adc	%Q0, %3, #0"			\
+				: "=&r" (__res)				\
+				: "r" (__m), "r" (__n), "r" (__z)	\
+				: "cc" );				\
+		}							\
+		if (!(__m & ((1ULL << 63) | (1ULL << 31)))) {		\
+			asm (	"umlal	%R0, %Q0, %R1, %Q2\n\t"		\
+				"umlal	%R0, %Q0, %Q1, %R2\n\t"		\
+				"mov	%R0, #0\n\t"			\
+				"umlal	%Q0, %R0, %R1, %R2"		\
+				: "+r" (__res)				\
+				: "r" (__m), "r" (__n)			\
+				: "cc" );				\
+		} else {						\
+			asm (	"umlal	%R0, %Q0, %R2, %Q3\n\t"		\
+				"umlal	%R0, %1, %Q2, %R3\n\t"		\
+				"mov	%R0, #0\n\t"			\
+				"adds	%Q0, %1, %Q0\n\t"		\
+				"adc	%R0, %R0, #0\n\t"		\
+				"umlal	%Q0, %R0, %R2, %R3"		\
+				: "+r" (__res), "+r" (__z)		\
+				: "r" (__m), "r" (__n)			\
+				: "cc" );				\
+		}							\
+		__res /= __p;						\
+		/* The reminder can be computed with 32-bit regs     */	\
+		/* only, and gcc is good at that.                    */	\
+		{							\
+			unsigned int __res0 = __res;			\
+			unsigned int __b0 = __b;			\
+			__r -= __res0 * __b0;				\
+		}							\
+		/* BUG_ON(__r >= __b || __res * __b + __r != n); */	\
+		n = __res;						\
+	}								\
+	__r;								\
+})
+
+/* our own fls implementation to make sure constant propagation is fine */
+#define __div64_fls(bits)						\
+({									\
+	unsigned int __left = (bits), __nr = 0;				\
+	if (__left & 0xffff0000) __nr += 16, __left >>= 16;		\
+	if (__left & 0x0000ff00) __nr +=  8, __left >>=  8;		\
+	if (__left & 0x000000f0) __nr +=  4, __left >>=  4;		\
+	if (__left & 0x0000000c) __nr +=  2, __left >>=  2;		\
+	if (__left & 0x00000002) __nr +=  1;				\
+	__nr;								\
+})
+
+#endif
+
 #endif