video/hdmi: Add Unpack only function for DRM infoframe

It adds an unpack only function for DRM infoframe for dynamic range and
mastering infoframe readout.
It unpacks the information data block contained in the binary buffer into
a structured frame of the HDMI Dynamic Range and Mastering (DRM)
information frame.

In contrast to hdmi_drm_infoframe_unpack() function, it does not verify
a checksum.

It can be used for unpacking a DP HDR Metadata Infoframe SDP case.
DP HDR Metadata Infoframe SDP uses the same Dynamic Range and Mastering
(DRM) information (CTA-861-G spec.) such as HDMI DRM infoframe.
But DP SDP header and payload structure are different from HDMI DRM
Infoframe. Therefore unpacking DRM infoframe for DP requires skipping of
a verifying checksum.

v9: Add clear comments to hdmi_drm_infoframe_unpack_only() and
    hdmi_drm_infoframe_unpack() (Laurent Pinchart)
Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200514060732.3378396-2-gwan-gyeong.mun@intel.com

drivers/video/hdmi.c

@@ -1768,20 +1768,21 @@ hdmi_vendor_any_infoframe_unpack(union hdmi_vendor_any_infoframe *frame,
 }
 
 /**
- * hdmi_drm_infoframe_unpack() - unpack binary buffer to a HDMI DRM infoframe
+ * hdmi_drm_infoframe_unpack_only() - unpack binary buffer of CTA-861-G DRM
+ *                                    infoframe DataBytes to a HDMI DRM
+ *                                    infoframe
  * @frame: HDMI DRM infoframe
  * @buffer: source buffer
  * @size: size of buffer
  *
- * Unpacks the information contained in binary @buffer into a structured
- * @frame of the HDMI Dynamic Range and Mastering (DRM) information frame.
- * Also verifies the checksum as required by section 5.3.5 of the HDMI 1.4
- * specification.
+ * Unpacks CTA-861-G DRM infoframe DataBytes contained in the binary @buffer
+ * into a structured @frame of the HDMI Dynamic Range and Mastering (DRM)
+ * infoframe.
  *
  * Returns 0 on success or a negative error code on failure.
  */
-static int hdmi_drm_infoframe_unpack(struct hdmi_drm_infoframe *frame,
-				     const void *buffer, size_t size)
+int hdmi_drm_infoframe_unpack_only(struct hdmi_drm_infoframe *frame,
+				   const void *buffer, size_t size)
 {
 	const u8 *ptr = buffer;
 	const u8 *temp;
@@ -1790,23 +1791,13 @@ static int hdmi_drm_infoframe_unpack(struct hdmi_drm_infoframe *frame,
 	int ret;
 	int i;
 
-	if (size < HDMI_INFOFRAME_SIZE(DRM))
-		return -EINVAL;
-
-	if (ptr[0] != HDMI_INFOFRAME_TYPE_DRM ||
-	    ptr[1] != 1 ||
-	    ptr[2] != HDMI_DRM_INFOFRAME_SIZE)
-		return -EINVAL;
-
-	if (hdmi_infoframe_checksum(buffer, HDMI_INFOFRAME_SIZE(DRM)) != 0)
+	if (size < HDMI_DRM_INFOFRAME_SIZE)
 		return -EINVAL;
 
 	ret = hdmi_drm_infoframe_init(frame);
 	if (ret)
 		return ret;
 
-	ptr += HDMI_INFOFRAME_HEADER_SIZE;
-
 	frame->eotf = ptr[0] & 0x7;
 	frame->metadata_type = ptr[1] & 0x7;
 
@@ -1814,7 +1805,7 @@ static int hdmi_drm_infoframe_unpack(struct hdmi_drm_infoframe *frame,
 	for (i = 0; i < 3; i++) {
 		x_lsb = *temp++;
 		x_msb = *temp++;
-		frame->display_primaries[i].x =  (x_msb << 8) | x_lsb;
+		frame->display_primaries[i].x = (x_msb << 8) | x_lsb;
 		y_lsb = *temp++;
 		y_msb = *temp++;
 		frame->display_primaries[i].y = (y_msb << 8) | y_lsb;
@@ -1830,6 +1821,42 @@ static int hdmi_drm_infoframe_unpack(struct hdmi_drm_infoframe *frame,
 
 	return 0;
 }
+EXPORT_SYMBOL(hdmi_drm_infoframe_unpack_only);
+
+/**
+ * hdmi_drm_infoframe_unpack() - unpack binary buffer to a HDMI DRM infoframe
+ * @frame: HDMI DRM infoframe
+ * @buffer: source buffer
+ * @size: size of buffer
+ *
+ * Unpacks the CTA-861-G DRM infoframe contained in the binary @buffer into
+ * a structured @frame of the HDMI Dynamic Range and Mastering (DRM)
+ * infoframe. It also verifies the checksum as required by section 5.3.5 of
+ * the HDMI 1.4 specification.
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+static int hdmi_drm_infoframe_unpack(struct hdmi_drm_infoframe *frame,
+				     const void *buffer, size_t size)
+{
+	const u8 *ptr = buffer;
+	int ret;
+
+	if (size < HDMI_INFOFRAME_SIZE(DRM))
+		return -EINVAL;
+
+	if (ptr[0] != HDMI_INFOFRAME_TYPE_DRM ||
+	    ptr[1] != 1 ||
+	    ptr[2] != HDMI_DRM_INFOFRAME_SIZE)
+		return -EINVAL;
+
+	if (hdmi_infoframe_checksum(buffer, HDMI_INFOFRAME_SIZE(DRM)) != 0)
+		return -EINVAL;
+
+	ret = hdmi_drm_infoframe_unpack_only(frame, ptr + HDMI_INFOFRAME_HEADER_SIZE,
+					     size - HDMI_INFOFRAME_HEADER_SIZE);
+	return ret;
+}
 
 /**
  * hdmi_infoframe_unpack() - unpack binary buffer to a HDMI infoframe

include/linux/hdmi.h

@@ -219,6 +219,8 @@ ssize_t hdmi_drm_infoframe_pack(struct hdmi_drm_infoframe *frame, void *buffer,
 ssize_t hdmi_drm_infoframe_pack_only(const struct hdmi_drm_infoframe *frame,
 				     void *buffer, size_t size);
 int hdmi_drm_infoframe_check(struct hdmi_drm_infoframe *frame);
+int hdmi_drm_infoframe_unpack_only(struct hdmi_drm_infoframe *frame,
+				   const void *buffer, size_t size);
 
 enum hdmi_spd_sdi {
 	HDMI_SPD_SDI_UNKNOWN,