From: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Date: Wed, 18 Apr 2018 14:11:43 -0400
Subject: drm/amd/display: add fixed point fractional bit truncation function
Git-commit: ab9c2062d960df84d41c03efc49cb01071b398c6
Patch-mainline: v4.18-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

Signed-off-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/amd/display/include/fixed31_32.h |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)

--- a/drivers/gpu/drm/amd/display/include/fixed31_32.h
+++ b/drivers/gpu/drm/amd/display/include/fixed31_32.h
@@ -496,4 +496,21 @@ unsigned int dc_fixpt_clamp_u0d10(struct
 
 int dc_fixpt_s4d19(struct fixed31_32 arg);
 
+static inline struct fixed31_32 dc_fixpt_truncate(struct fixed31_32 arg, unsigned int frac_bits)
+{
+	bool negative = arg.value < 0;
+
+	if (frac_bits >= FIXED31_32_BITS_PER_FRACTIONAL_PART) {
+		ASSERT(frac_bits == FIXED31_32_BITS_PER_FRACTIONAL_PART);
+		return arg;
+	}
+
+	if (negative)
+		arg.value = -arg.value;
+	arg.value &= (~0LL) << (FIXED31_32_BITS_PER_FRACTIONAL_PART - frac_bits);
+	if (negative)
+		arg.value = -arg.value;
+	return arg;
+}
+
 #endif