drm/komeda: Add drm_ctm_to_coeffs()

This function is for converting drm_color_ctm matrix to komeda hardware
required required Q2.12 2's complement CSC matrix.

v2:
  Move the fixpoint conversion function s31_32_to_q2_12() to drm core
  as a shared helper.
Signed-off-by: james qian wang (Arm Technology China) <james.qian.wang@arm.com>
Reviewed-by: Mihail Atanassov <mihail.atanassov@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191112110927.20931-4-james.qian.wang@arm.com

drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.c

@@ -117,3 +117,17 @@ void drm_lut_to_fgamma_coeffs(struct drm_property_blob *lut_blob, u32 *coeffs)
 {
 	drm_lut_to_coeffs(lut_blob, coeffs, sector_tbl, ARRAY_SIZE(sector_tbl));
 }
+
+void drm_ctm_to_coeffs(struct drm_property_blob *ctm_blob, u32 *coeffs)
+{
+	struct drm_color_ctm *ctm;
+	u32 i;
+
+	if (!ctm_blob)
+		return;
+
+	ctm = ctm_blob->data;
+
+	for (i = 0; i < KOMEDA_N_CTM_COEFFS; i++)
+		coeffs[i] = drm_color_ctm_s31_32_to_qm_n(ctm->matrix[i], 3, 12);
+}

drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.h

@@ -18,6 +18,7 @@
 #define KOMEDA_N_CTM_COEFFS		9
 
 void drm_lut_to_fgamma_coeffs(struct drm_property_blob *lut_blob, u32 *coeffs);
+void drm_ctm_to_coeffs(struct drm_property_blob *ctm_blob, u32 *coeffs);
 
 const s32 *komeda_select_yuv2rgb_coeffs(u32 color_encoding, u32 color_range);