media: doc-rst: add more info for resolution change blocks in ipu3

This patch add more details for the resolution change blocks
It can help the developer to understand the main resolution
change blocks in ImgU.

[sakari.ailus@linux.intel.com: Add new files to MAINTAINERS]

Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

Documentation/media/v4l-drivers/ipu3.rst

@@ -265,19 +265,56 @@ below.
 
 yavta -w "0x009819A1 1" /dev/v4l-subdev7
 
-RAW Bayer frames go through the following ImgU pipeline HW blocks to have the
+Certain hardware blocks in ImgU pipeline can change the frame resolution by
+cropping or scaling, these hardware blocks include Input Feeder(IF), Bayer Down
+Scaler (BDS) and Geometric Distortion Correction (GDC).
+There is also a block which can change the frame resolution - YUV Scaler, it is
+only applicable to the secondary output.
+
+RAW Bayer frames go through these ImgU pipeline hardware blocks and the final
 processed image output to the DDR memory.
 
-RAW Bayer frame -> Input Feeder -> Bayer Down Scaling (BDS) -> Geometric
-Distortion Correction (GDC) -> DDR
+.. kernel-figure::  ipu3_rcb.svg
+   :alt: ipu3 resolution blocks image
 
-The ImgU V4L2 subdev has to be configured with the supported resolutions in all
-the above HW blocks, for a given input resolution.
+   IPU3 resolution change hardware blocks
+
+**Input Feeder**
+
+Input Feeder gets the Bayer frame data from the sensor, it can enable cropping
+of lines and columns from the frame and then store pixels into device's internal
+pixel buffer which are ready to readout by following blocks.
+
+**Bayer Down Scaler**
+
+Bayer Down Scaler is capable of performing image scaling in Bayer domain, the
+downscale factor can be configured from 1X to 1/4X in each axis with
+configuration steps of 0.03125 (1/32).
 
+**Geometric Distortion Correction**
+
+Geometric Distortion Correction is used to performe correction of distortions
+and image filtering. It needs some extra filter and envelop padding pixels to
+work, so the input resolution of GDC should be larger than the output
+resolution.
+
+**YUV Scaler**
+
+YUV Scaler which similar with BDS, but it is mainly do image down scaling in
+YUV domain, it can support up to 1/12X down scaling, but it can not be applied
+to the main output.
+
+The ImgU V4L2 subdev has to be configured with the supported resolutions in all
+the above hardware blocks, for a given input resolution.
 For a given supported resolution for an input frame, the Input Feeder, Bayer
-Down Scaling and GDC blocks should be configured with the supported resolutions.
-This information can be obtained by looking at the following IPU3 ImgU
-configuration table.
+Down Scaler and GDC blocks should be configured with the supported resolutions
+as each hardware block has its own alignment requirement.
+
+You must configure the output resolution of the hardware blocks smartly to meet
+the hardware requirement along with keeping the maximum field of view.
+The intermediate resolutions can be generated by specific tool and this
+information can be obtained by looking at the following IPU3 ImgU configuration
+table.
 
 https://chromium.googlesource.com/chromiumos/overlays/board-overlays/+/master