[PATCH v7 2/8] media: jpeg: Add JPEG baseline and JFIF APP0 constants

[Atanas Filipov]

Add the standard field values of a baseline (ITU-T T.81) JFIF header
to the shared JPEG marker header: sample precision, component counts,
sampling factors, quantization table identifiers, SOS table selectors,
spectral selection and successive approximation and the JFIF APP0
payload values. Describe the marker segment header and the SOF0 and
SOS headers and component specifications as packed structs, so their
sizes and field offsets can be taken with sizeof() and offsetof().

Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
Signed-off-by: Atanas Filipov <atanas.filipov@xxxxxxxxxxxxxxxx>
---
 include/media/jpeg.h | 79 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/include/media/jpeg.h b/include/media/jpeg.h
index a01e142e99a7d..a93d0a580bbe3 100644
--- a/include/media/jpeg.h
+++ b/include/media/jpeg.h
@@ -3,6 +3,8 @@
 #ifndef _MEDIA_JPEG_H_
 #define _MEDIA_JPEG_H_
 
+#include <linux/types.h>
+
 /* JPEG markers */
 #define JPEG_MARKER_TEM		0x01
 #define JPEG_MARKER_SOF0	0xc0
@@ -17,4 +19,81 @@
 #define JPEG_MARKER_APP0	0xe0
 #define JPEG_MARKER_COM		0xfe
 
+/* JPEG baseline sample precision (bits per sample) */
+#define JPEG_SAMPLE_PRECISION_BITS	8
+
+/* Number of components: greyscale (1) and colour YCbCr (3) */
+#define JPEG_COMP_MONO			1
+#define JPEG_COMP_COLOR			3
+
+/* Chroma subsampling factors encoded in SOF0 sampling byte */
+#define JPEG_SAMPLING_H1V1		0x11
+#define JPEG_SAMPLING_H2V2		0x22
+
+/* Quantization table destination identifiers */
+#define JPEG_QTABLE_LUMA		0
+#define JPEG_QTABLE_CHROMA		1
+
+/* SOS spectral selection and approximation fields (baseline JPEG) */
+#define JPEG_SPECTRAL_START		0x00
+#define JPEG_SPECTRAL_END		0x3f
+#define JPEG_APPROX_HIGH_LOW		0x00
+
+/* SOS table selector bytes (luma: DC=0/AC=0, chroma: DC=1/AC=1) */
+#define JPEG_TABLE_SEL_LUMA		0x00
+#define JPEG_TABLE_SEL_CHROMA		0x11
+
+/*
+ * JFIF APP0 payload fields, as specified by the JFIF spec referenced from
+ * ITU-T T.81 Annex B. See: https://www.w3.org/Graphics/JPEG/itu-t81.pdf
+ */
+#define JFIF_IDENT_TERM			0x00
+#define JFIF_VERSION_MAJOR		0x01
+#define JFIF_VERSION_MINOR		0x01
+#define JFIF_UNITS_NONE			0x00
+#define JFIF_DENSITY_HI			0x00
+#define JFIF_DENSITY_LO			0x01
+#define JFIF_THUMBNAIL_SIZE		0x00
+
+/* Marker segment header: marker and length (ITU-T T.81 B.1.1.4) */
+struct jpeg_seg_hdr {
+	__be16 marker;
+	__be16 length;	/* bytes from the length field to the end of the segment */
+} __packed;
+
+/* SOF0 frame header up to the component specifications (ITU-T T.81 B.2.2) */
+struct jpeg_sof_hdr {
+	struct jpeg_seg_hdr seg;
+	u8 precision;
+	__be16 height;
+	__be16 width;
+	u8 num_components;
+} __packed;
+
+/* SOF0 frame component specification, one per component */
+struct jpeg_sof_comp {
+	u8 id;
+	u8 sampling;
+	u8 qtable;
+} __packed;
+
+/* SOS scan header up to the component specifications (ITU-T T.81 B.2.3) */
+struct jpeg_sos_hdr {
+	struct jpeg_seg_hdr seg;
+	u8 num_components;
+} __packed;
+
+/* SOS scan component specification, one per component */
+struct jpeg_sos_comp {
+	u8 id;
+	u8 tables;	/* DC and AC entropy table selectors */
+} __packed;
+
+/* SOS fields after the component specifications */
+struct jpeg_sos_tail {
+	u8 spectral_start;
+	u8 spectral_end;
+	u8 approx;
+} __packed;
+
 #endif /* _MEDIA_JPEG_H_ */
-- 
2.34.1