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+.. SPDX-License-Identifier: GPL-2.0
+
+=========================================
+Rockchip Camera Interface (CIF)
+=========================================
+
+Introduction
+============
+
+The Rockchip Camera Interface (CIF) is featured in many Rockchip SoCs in
+different variants.
+The different variants are combinations of common building blocks, such as
+
+* INTERFACE blocks of different types, namely
+
+  * the Digital Video Port (DVP, a parallel data interface)
+  * the interface block for the MIPI CSI-2 receiver
+
+* CROP units
+
+* MIPI CSI-2 receiver (not available on all variants): This unit is referred
+  to as MIPI CSI HOST in the Rockchip documentation.
+  Technically, it is a separate hardware block, but it is strongly coupled to
+  the CIF and therefore included here.
+
+* MUX units (not available on all variants) that pass the video data to an
+  image signal processor (ISP)
+
+* SCALE units (not available on all variants)
+
+* DMA engines that transfer video data into system memory using a
+  double-buffering mechanism called ping-pong mode
+
+* Support for four streams per INTERFACE block (not available on all
+  variants), e.g., for MIPI CSI-2 Virtual Channels (VCs)
+
+This document describes the different variants of the CIF, their hardware
+layout, as well as their representation in the media controller centric rkcif
+device driver, which is located under drivers/media/platform/rockchip/rkcif.
+
+Variants
+========
+
+Rockchip PX30 Video Input Processor (VIP)
+-----------------------------------------
+
+The PX30 Video Input Processor (VIP) features a digital video port that accepts
+parallel video data or BT.656.
+Since these protocols do not feature multiple streams, the VIP has one DMA
+engine that transfers the input video data into system memory.
+
+The rkcif driver represents this hardware variant by exposing one V4L2 subdevice
+(the DVP INTERFACE/CROP block) and one V4L2 device (the DVP DMA engine).
+
+Rockchip RK3568 Video Capture (VICAP)
+-------------------------------------
+
+The RK3568 Video Capture (VICAP) unit features a digital video port and a MIPI
+CSI-2 receiver that can receive video data independently.
+The DVP accepts parallel video data, BT.656 and BT.1120.
+Since the BT.1120 protocol may feature more than one stream, the RK3568 VICAP
+DVP features four DMA engines that can capture different streams.
+Similarly, the RK3568 VICAP MIPI CSI-2 receiver features four DMA engines to
+handle different Virtual Channels (VCs).
+
+The rkcif driver represents this hardware variant by exposing up the following
+V4L2 subdevices:
+
+* rkcif-dvp0: INTERFACE/CROP block for the DVP
+
+and the following video devices:
+
+* rkcif-dvp0-id0: The support for multiple streams on the DVP is not yet
+  implemented, as it is hard to find test hardware. Thus, this video device
+  represents the first DMA engine of the RK3568 DVP.
+
+.. kernel-figure:: rkcif-rk3568-vicap.dot
+    :alt:   Topology of the RK3568 Video Capture (VICAP) unit
+    :align: center