media: atmel: atmel-isc: reworked white balance feature

Reworked auto white balance feature (awb) to cope with all four channels.
Implemented stretching and grey world algorithms.
Using the histogram, the ISC will auto adjust the white balance during
frame captures.
Because each histogram needs a frame, it will take 4 frames for one adjustment.
When the gains were updated by previous code, the registers for the gains
were updated only on new streaming start. Now, after each full histogram the
registers are updated with new gains.
Also, on previous code, if the streaming stopped but not all 3 histograms
finished, a new histogram was started either way. This used to lead to an
error "timeout to update profile" when streaming was stopped.
According to the hardware, histogram can only work together with the capture,
not independently.
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/platform/atmel/atmel-isc-regs.h

@@ -100,13 +100,15 @@
 #define ISC_WB_O_RGR	0x00000060
 
 /* ISC White Balance Offset for B, GB Register */
-#define ISC_WB_O_BGR	0x00000064
+#define ISC_WB_O_BGB	0x00000064
 
 /* ISC White Balance Gain for R, GR Register */
 #define ISC_WB_G_RGR	0x00000068
 
 /* ISC White Balance Gain for B, GB Register */
-#define ISC_WB_G_BGR	0x0000006c
+#define ISC_WB_G_BGB	0x0000006c
+
+#define ISC_WB_O_ZERO_VAL	(1 << 13)
 
 /* ISC Color Filter Array Control Register */
 #define ISC_CFA_CTRL    0x00000070