From 7ce5b6850b47824a2b8d0a17b5fe75f9942e5cd1 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Wed, 13 Sep 2017 11:51:54 +0100
Subject: [PATCH] drm/i915/selftests: Use mul_u32_u32() for 32b x 32b -> 64b result
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Git-commit: 7ce5b6850b47824a2b8d0a17b5fe75f9942e5cd1
Patch-mainline: v4.15-rc1
References: FATE#322643 bsc#1055900

As realised by commit 9e3d6223d209 ("math64, timers: Fix 32bit
mul_u64_u32_shr() and friends"), GCC does not always generate ideal code
for performing a 32b x 32b multiply returning a 64b result (i.e. where
we idiomatically use u64 result = (u64)x * (u32)x).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20170913105154.2910-2-chris@chris-wilson.co.uk
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/i915/selftests/i915_gem_timeline.c |    2 +-
 drivers/gpu/drm/i915/selftests/i915_random.c       |    5 -----
 drivers/gpu/drm/i915/selftests/i915_random.h       |    5 +++++
 3 files changed, 6 insertions(+), 6 deletions(-)

--- a/drivers/gpu/drm/i915/selftests/i915_gem_timeline.c
+++ b/drivers/gpu/drm/i915/selftests/i915_gem_timeline.c
@@ -121,7 +121,7 @@ out:
 
 static unsigned int random_engine(struct rnd_state *rnd)
 {
-	return ((u64)prandom_u32_state(rnd) * I915_NUM_ENGINES) >> 32;
+	return i915_prandom_u32_max_state(I915_NUM_ENGINES, rnd);
 }
 
 static int bench_sync(void *arg)
--- a/drivers/gpu/drm/i915/selftests/i915_random.c
+++ b/drivers/gpu/drm/i915/selftests/i915_random.c
@@ -41,11 +41,6 @@ u64 i915_prandom_u64_state(struct rnd_st
 	return x;
 }
 
-static inline u32 i915_prandom_u32_max_state(u32 ep_ro, struct rnd_state *state)
-{
-	return upper_32_bits((u64)prandom_u32_state(state) * ep_ro);
-}
-
 void i915_random_reorder(unsigned int *order, unsigned int count,
 			 struct rnd_state *state)
 {
--- a/drivers/gpu/drm/i915/selftests/i915_random.h
+++ b/drivers/gpu/drm/i915/selftests/i915_random.h
@@ -43,6 +43,11 @@
 
 u64 i915_prandom_u64_state(struct rnd_state *rnd);
 
+static inline u32 i915_prandom_u32_max_state(u32 ep_ro, struct rnd_state *state)
+{
+	return upper_32_bits(mul_u32_u32(prandom_u32_state(state), ep_ro));
+}
+
 unsigned int *i915_random_order(unsigned int count,
 				struct rnd_state *state);
 void i915_random_reorder(unsigned int *order,