media: Documentation: Include CCS PLL calculator to CCS driver documentation

Include existing CCS PLL calculator kerneldoc documentation to the
documentation build.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

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

@@ -79,4 +79,17 @@ definitions:
 		-l drivers/media/i2c/ccs/ccs-limits.c \
 		-c Documentation/driver-api/media/drivers/ccs/ccs-regs.asc
 
+CCS PLL calculator
+==================
+
+The CCS PLL calculator is used to compute the PLL configuration, given sensor's
+capabilities as well as board configuration and user specified configuration. As
+the configuration space that encompasses all these configurations is vast, the
+PLL calculator isn't entirely trivial. Yet it is relatively simple to use for a
+driver.
+
+The PLL model implemented by the PLL calculator corresponds to MIPI CCS 1.1.
+
+.. kernel-doc:: drivers/media/i2c/ccs-pll.h
+
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