1 files changed, 8 insertions, 11 deletions
diff --git a/include/drm/drm_color_mgmt.h b/include/drm/drm_color_mgmt.h
index 81c298488b0c..54b2b2467bfd 100644
--- a/include/drm/drm_color_mgmt.h
+++ b/include/drm/drm_color_mgmt.h
@@ -36,20 +36,17 @@ struct drm_plane;
  *
  * Extract a degamma/gamma LUT value provided by user (in the form of
  * &drm_color_lut entries) and round it to the precision supported by the
- * hardware.
+ * hardware, following OpenGL int<->float conversion rules
+ * (see eg. OpenGL 4.6 specification - 2.3.5 Fixed-Point Data Conversions).
  */
 static inline u32 drm_color_lut_extract(u32 user_input, int bit_precision)
 {
-	u32 val = user_input;
-	u32 max = 0xffff >> (16 - bit_precision);
-
-	/* Round only if we're not using full precision. */
-	if (bit_precision < 16) {
-		val += 1UL << (16 - bit_precision - 1);
-		val >>= 16 - bit_precision;
-	}
-
-	return clamp_val(val, 0, max);
+	if (bit_precision > 16)
+		return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(user_input, (1 << bit_precision) - 1),
+					     (1 << 16) - 1);
+	else
+		return DIV_ROUND_CLOSEST(user_input * ((1 << bit_precision) - 1),
+					 (1 << 16) - 1);
 }
 
 u64 drm_color_ctm_s31_32_to_qm_n(u64 user_input, u32 m, u32 n);