media: v4l: uapi: ccs: Add controls for CCS alternative analogue gain

Add two new controls for alternative analogue gain some CCS compliant
camera sensors support.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/userspace-api/media/drivers/ccs.rst

@@ -81,4 +81,17 @@ obtained from the following controls:
 The analogue gain (``x`` in the formula) is controlled through
 ``V4L2_CID_ANALOGUE_GAIN`` in this case.
 
+Alternate analogue gain model
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The CCS defines another analogue gain model called alternate analogue gain. In
+this case, the formula to calculate actual gain consists of linear and
+exponential parts:
+
+	gain = linear * 2 ^ exponent
+
+The ``linear`` and ``exponent`` factors can be set using the
+``V4L2_CID_CCS_ANALOGUE_LINEAR_GAIN`` and
+``V4L2_CID_CCS_ANALOGUE_EXPONENTIAL_GAIN`` controls, respectively
+
 **Copyright** |copy| 2020 Intel Corporation

include/uapi/linux/ccs.h

@@ -10,5 +10,7 @@
 #define V4L2_CID_CCS_ANALOGUE_GAIN_C0		(V4L2_CID_USER_CCS_BASE + 2)
 #define V4L2_CID_CCS_ANALOGUE_GAIN_M1		(V4L2_CID_USER_CCS_BASE + 3)
 #define V4L2_CID_CCS_ANALOGUE_GAIN_C1		(V4L2_CID_USER_CCS_BASE + 4)
+#define V4L2_CID_CCS_ANALOGUE_LINEAR_GAIN	(V4L2_CID_USER_CCS_BASE + 5)
+#define V4L2_CID_CCS_ANALOGUE_EXPONENTIAL_GAIN	(V4L2_CID_USER_CCS_BASE + 6)
 
 #endif