[media] cx2341x: add contents of README.hm12

The README.hm12 file describes the proprietary format used
by this driver for raw format, called HM12. Add its description
at the document, after converted to ReST.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

1 files changed, 125 insertions, 0 deletions

diff --git a/Documentation/media/v4l-drivers/cx2341x.rst b/Documentation/media/v4l-drivers/cx2341x.rst
index 57ae45938919..15bfd345df48 100644
--- a/Documentation/media/v4l-drivers/cx2341x.rst
+++ b/Documentation/media/v4l-drivers/cx2341x.rst
@@ -3681,3 +3681,128 @@ Register 0x0004 holds the DMA Transfer Status:
 - bit 2:   DMA read error
 - bit 3:   DMA write error
 - bit 4:   Scatter-Gather array error
+
+Non-compressed file format
+--------------------------
+
+The cx23416 can produce (and the cx23415 can also read) raw YUV output. The
+format of a YUV frame is specific to this chip and is called HM12. 'HM' stands
+for 'Hauppauge Macroblock', which is a misnomer as 'Conexant Macroblock' would
+be more accurate.
+
+The format is YUV 4:2:0 which uses 1 Y byte per pixel and 1 U and V byte per
+four pixels.
+
+The data is encoded as two macroblock planes, the first containing the Y
+values, the second containing UV macroblocks.
+
+The Y plane is divided into blocks of 16x16 pixels from left to right
+and from top to bottom. Each block is transmitted in turn, line-by-line.
+
+So the first 16 bytes are the first line of the top-left block, the
+second 16 bytes are the second line of the top-left block, etc. After
+transmitting this block the first line of the block on the right to the
+first block is transmitted, etc.
+
+The UV plane is divided into blocks of 16x8 UV values going from left
+to right, top to bottom. Each block is transmitted in turn, line-by-line.
+
+So the first 16 bytes are the first line of the top-left block and
+contain 8 UV value pairs (16 bytes in total). The second 16 bytes are the
+second line of 8 UV pairs of the top-left block, etc. After transmitting
+this block the first line of the block on the right to the first block is
+transmitted, etc.
+
+The code below is given as an example on how to convert HM12 to separate
+Y, U and V planes. This code assumes frames of 720x576 (PAL) pixels.
+
+The width of a frame is always 720 pixels, regardless of the actual specified
+width.
+
+If the height is not a multiple of 32 lines, then the captured video is
+missing macroblocks at the end and is unusable. So the height must be a
+multiple of 32.
+
+Raw format c example
+~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
+	#include <stdio.h>
+	#include <stdlib.h>
+	#include <string.h>
+
+	static unsigned char frame[576*720*3/2];
+	static unsigned char framey[576*720];
+	static unsigned char frameu[576*720 / 4];
+	static unsigned char framev[576*720 / 4];
+
+	static void de_macro_y(unsigned char* dst, unsigned char *src, int dstride, int w, int h)
+	{
+	unsigned int y, x, i;
+
+	// descramble Y plane
+	// dstride = 720 = w
+	// The Y plane is divided into blocks of 16x16 pixels
+	// Each block in transmitted in turn, line-by-line.
+	for (y = 0; y < h; y += 16) {
+		for (x = 0; x < w; x += 16) {
+		for (i = 0; i < 16; i++) {
+			memcpy(dst + x + (y + i) * dstride, src, 16);
+			src += 16;
+		}
+		}
+	}
+	}
+
+	static void de_macro_uv(unsigned char *dstu, unsigned char *dstv, unsigned char *src, int dstride, int w, int h)
+	{
+	unsigned int y, x, i;
+
+	// descramble U/V plane
+	// dstride = 720 / 2 = w
+	// The U/V values are interlaced (UVUV...).
+	// Again, the UV plane is divided into blocks of 16x16 UV values.
+	// Each block in transmitted in turn, line-by-line.
+	for (y = 0; y < h; y += 16) {
+		for (x = 0; x < w; x += 8) {
+		for (i = 0; i < 16; i++) {
+			int idx = x + (y + i) * dstride;
+
+			dstu[idx+0] = src[0];  dstv[idx+0] = src[1];
+			dstu[idx+1] = src[2];  dstv[idx+1] = src[3];
+			dstu[idx+2] = src[4];  dstv[idx+2] = src[5];
+			dstu[idx+3] = src[6];  dstv[idx+3] = src[7];
+			dstu[idx+4] = src[8];  dstv[idx+4] = src[9];
+			dstu[idx+5] = src[10]; dstv[idx+5] = src[11];
+			dstu[idx+6] = src[12]; dstv[idx+6] = src[13];
+			dstu[idx+7] = src[14]; dstv[idx+7] = src[15];
+			src += 16;
+		}
+		}
+	}
+	}
+
+	/*************************************************************************/
+	int main(int argc, char **argv)
+	{
+	FILE *fin;
+	int i;
+
+	if (argc == 1) fin = stdin;
+	else fin = fopen(argv[1], "r");
+
+	if (fin == NULL) {
+		fprintf(stderr, "cannot open input\n");
+		exit(-1);
+	}
+	while (fread(frame, sizeof(frame), 1, fin) == 1) {
+		de_macro_y(framey, frame, 720, 720, 576);
+		de_macro_uv(frameu, framev, frame + 720 * 576, 720 / 2, 720 / 2, 576 / 2);
+		fwrite(framey, sizeof(framey), 1, stdout);
+		fwrite(framev, sizeof(framev), 1, stdout);
+		fwrite(frameu, sizeof(frameu), 1, stdout);
+	}
+	fclose(fin);
+	return 0;
+	}