V4L/DVB (9242): video: add sh_mobile_ceu comments

This patch adds CEU hardware block comments to the sh_mobile_ceu driver.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/sh_mobile_ceu_camera.c

@@ -40,39 +40,39 @@
 
 /* register offsets for sh7722 / sh7723 */
 
-#define CAPSR  0x00
+#define CAPSR  0x00 /* Capture start register */
-#define CAPCR  0x04
+#define CAPCR  0x04 /* Capture control register */
-#define CAMCR  0x08
+#define CAMCR  0x08 /* Capture interface control register */
-#define CMCYR  0x0c
+#define CMCYR  0x0c /* Capture interface cycle  register */
-#define CAMOR  0x10
+#define CAMOR  0x10 /* Capture interface offset register */
-#define CAPWR  0x14
+#define CAPWR  0x14 /* Capture interface width register */
-#define CAIFR  0x18
+#define CAIFR  0x18 /* Capture interface input format register */
-#define CSTCR  0x20 /* not on sh7723 */
+#define CSTCR  0x20 /* Camera strobe control register (<= sh7722) */
-#define CSECR  0x24 /* not on sh7723 */
+#define CSECR  0x24 /* Camera strobe emission count register (<= sh7722) */
-#define CRCNTR 0x28
+#define CRCNTR 0x28 /* CEU register control register */
-#define CRCMPR 0x2c
+#define CRCMPR 0x2c /* CEU register forcible control register */
-#define CFLCR  0x30
+#define CFLCR  0x30 /* Capture filter control register */
-#define CFSZR  0x34
+#define CFSZR  0x34 /* Capture filter size clip register */
-#define CDWDR  0x38
+#define CDWDR  0x38 /* Capture destination width register */
-#define CDAYR  0x3c
+#define CDAYR  0x3c /* Capture data address Y register */
-#define CDACR  0x40
+#define CDACR  0x40 /* Capture data address C register */
-#define CDBYR  0x44
+#define CDBYR  0x44 /* Capture data bottom-field address Y register */
-#define CDBCR  0x48
+#define CDBCR  0x48 /* Capture data bottom-field address C register */
-#define CBDSR  0x4c
+#define CBDSR  0x4c /* Capture bundle destination size register */
-#define CFWCR  0x5c
+#define CFWCR  0x5c /* Firewall operation control register */
-#define CLFCR  0x60
+#define CLFCR  0x60 /* Capture low-pass filter control register */
-#define CDOCR  0x64
+#define CDOCR  0x64 /* Capture data output control register */
-#define CDDCR  0x68
+#define CDDCR  0x68 /* Capture data complexity level register */
-#define CDDAR  0x6c
+#define CDDAR  0x6c /* Capture data complexity level address register */
-#define CEIER  0x70
+#define CEIER  0x70 /* Capture event interrupt enable register */
-#define CETCR  0x74
+#define CETCR  0x74 /* Capture event flag clear register */
-#define CSTSR  0x7c
+#define CSTSR  0x7c /* Capture status register */
-#define CSRTR  0x80
+#define CSRTR  0x80 /* Capture software reset register */
-#define CDSSR  0x84
+#define CDSSR  0x84 /* Capture data size register */
-#define CDAYR2 0x90
+#define CDAYR2 0x90 /* Capture data address Y register 2 */
-#define CDACR2 0x94
+#define CDACR2 0x94 /* Capture data address C register 2 */
-#define CDBYR2 0x98
+#define CDBYR2 0x98 /* Capture data bottom-field address Y register 2 */
-#define CDBCR2 0x9c
+#define CDBCR2 0x9c /* Capture data bottom-field address C register 2 */
 
 static DEFINE_MUTEX(camera_lock);
 
@@ -391,6 +391,19 @@ static int sh_mobile_ceu_set_bus_param(struct soc_camera_device *icd,
 	ceu_write(pcdev, CFLCR, 0); /* data fetch mode - no scaling */
 	ceu_write(pcdev, CFSZR, (icd->height << 16) | cfszr_width);
 	ceu_write(pcdev, CLFCR, 0); /* data fetch mode - no lowpass filter */
+
+	/* A few words about byte order (observed in Big Endian mode)
+	 *
+	 * In data fetch mode bytes are received in chunks of 8 bytes.
+	 * D0, D1, D2, D3, D4, D5, D6, D7 (D0 received first)
+	 *
+	 * The data is however by default written to memory in reverse order:
+	 * D7, D6, D5, D4, D3, D2, D1, D0 (D7 written to lowest byte)
+	 *
+	 * The lowest three bits of CDOCR allows us to do swapping,
+	 * right now we swap the data bytes to the following order:
+	 * D1, D0, D3, D2, D5, D4, D7, D6
+	 */
 	ceu_write(pcdev, CDOCR, 0x00000016);
 
 	ceu_write(pcdev, CDWDR, cdwdr_width);