From 9e3d6223d2093a8903c8f570a06284453ee59944 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Fri, 9 Dec 2016 09:30:11 +0100
Subject: math64, timers: Fix 32bit mul_u64_u32_shr() and friends

It turns out that while GCC-4.4 manages to generate 32x32->64 mult
instructions for the 32bit mul_u64_u32_shr() code, any GCC after that
fails horribly.

Fix this by providing an explicit mul_u32_u32() function which can be
architcture provided.

Reported-by: Chris Metcalf <cmetcalf@mellanox.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Chris Metcalf <cmetcalf@mellanox.com> [for tile]
Cc: Christopher S. Hall <christopher.s.hall@intel.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Laurent Vivier <lvivier@redhat.com>
Cc: Liav Rehana <liavr@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Parit Bhargava <prarit@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20161209083011.GD15765@worktop.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/div64.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

(limited to 'arch/x86/include/asm/div64.h')

diff --git a/arch/x86/include/asm/div64.h b/arch/x86/include/asm/div64.h
index ced283ac79df..af95c47d5c9e 100644
--- a/arch/x86/include/asm/div64.h
+++ b/arch/x86/include/asm/div64.h
@@ -59,6 +59,17 @@ static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
 }
 #define div_u64_rem	div_u64_rem
 
+static inline u64 mul_u32_u32(u32 a, u32 b)
+{
+	u32 high, low;
+
+	asm ("mull %[b]" : "=a" (low), "=d" (high)
+			 : [a] "a" (a), [b] "rm" (b) );
+
+	return low | ((u64)high) << 32;
+}
+#define mul_u32_u32 mul_u32_u32
+
 #else
 # include <asm-generic/div64.h>
 #endif /* CONFIG_X86_32 */
-- 
cgit