media: v4l: uapi: ccs: Add controls for analogue gain constants

Add V4L2 controls for analogue gain constants required to control
analogue gain. The values are device specific and thus need to be obtained
from the driver.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

1 files changed, 25 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/drivers/ccs.rst b/Documentation/userspace-api/media/drivers/ccs.rst
index 00bb3a6288f5..a95d7941533d 100644
--- a/Documentation/userspace-api/media/drivers/ccs.rst
+++ b/Documentation/userspace-api/media/drivers/ccs.rst
@@ -56,4 +56,29 @@ analogue data is never read from the pixel matrix that are outside the
 configured selection rectangle that designates crop. The difference has an
 effect in device timing and likely also in power consumption.
 
+Private controls
+----------------
+
+The MIPI CCS driver implements a number of private controls under
+``V4L2_CID_USER_BASE_CCS`` to control the MIPI CCS compliant camera sensors.
+
+Analogue gain model
+~~~~~~~~~~~~~~~~~~~
+
+The CCS defines an analogue gain model where the gain can be calculated using
+the following formula:
+
+	gain = m0 * x + c0 / (m1 * x + c1)
+
+Either m0 or c0 will be zero. The constants that are device specific, can be
+obtained from the following controls:
+
+	V4L2_CID_CCS_ANALOGUE_GAIN_M0
+	V4L2_CID_CCS_ANALOGUE_GAIN_M1
+	V4L2_CID_CCS_ANALOGUE_GAIN_C0
+	V4L2_CID_CCS_ANALOGUE_GAIN_C1
+
+The analogue gain (``x`` in the formula) is controlled through
+``V4L2_CID_ANALOGUE_GAIN`` in this case.
+
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