media: imx7.rst: add documentation for i.MX7 media driver

Add rst document to describe the i.MX7 media driver and also a working
example from the Warp7 board usage with a OV2680 sensor.
Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/media/v4l-drivers/imx7.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+i.MX7 Video Capture Driver
+==========================
+
+Introduction
+------------
+
+The i.MX7 contrary to the i.MX5/6 family does not contain an Image Processing
+Unit (IPU); because of that the capabilities to perform operations or
+manipulation of the capture frames are less feature rich.
+
+For image capture the i.MX7 has three units:
+- CMOS Sensor Interface (CSI)
+- Video Multiplexer
+- MIPI CSI-2 Receiver
+
+::
+                                           |\
+   MIPI Camera Input ---> MIPI CSI-2 --- > | \
+                                           |  \
+                                           | M |
+                                           | U | ------>  CSI ---> Capture
+                                           | X |
+                                           |  /
+   Parallel Camera Input ----------------> | /
+                                           |/
+
+For additional information, please refer to the latest versions of the i.MX7
+reference manual [#f1]_.
+
+Entities
+--------
+
+imx7-mipi-csi2
+--------------
+
+This is the MIPI CSI-2 receiver entity. It has one sink pad to receive the pixel
+data from MIPI CSI-2 camera sensor. It has one source pad, corresponding to the
+virtual channel 0. This module is compliant to previous version of Samsung
+D-phy, and supports two D-PHY Rx Data lanes.
+
+csi_mux
+-------
+
+This is the video multiplexer. It has two sink pads to select from either camera
+sensor with a parallel interface or from MIPI CSI-2 virtual channel 0.  It has
+a single source pad that routes to the CSI.
+
+csi
+---
+
+The CSI enables the chip to connect directly to external CMOS image sensor. CSI
+can interface directly with Parallel and MIPI CSI-2 buses. It has 256 x 64 FIFO
+to store received image pixel data and embedded DMA controllers to transfer data
+from the FIFO through AHB bus.
+
+This entity has one sink pad that receives from the csi_mux entity and a single
+source pad that routes video frames directly to memory buffers. This pad is
+routed to a capture device node.
+
+Usage Notes
+-----------
+
+To aid in configuration and for backward compatibility with V4L2 applications
+that access controls only from video device nodes, the capture device interfaces
+inherit controls from the active entities in the current pipeline, so controls
+can be accessed either directly from the subdev or from the active capture
+device interface. For example, the sensor controls are available either from the
+sensor subdevs or from the active capture device.
+
+Warp7 with OV2680
+-----------------
+
+On this platform an OV2680 MIPI CSI-2 module is connected to the internal MIPI
+CSI-2 receiver. The following example configures a video capture pipeline with
+an output of 800x600, and BGGR 10 bit bayer format:
+
+.. code-block:: none
+   # Setup links
+   media-ctl -l "'ov2680 1-0036':0 -> 'imx7-mipi-csis.0':0[1]"
+   media-ctl -l "'imx7-mipi-csis.0':1 -> 'csi_mux':1[1]"
+   media-ctl -l "'csi_mux':2 -> 'csi':0[1]"
+   media-ctl -l "'csi':1 -> 'csi capture':0[1]"
+
+   # Configure pads for pipeline
+   media-ctl -V "'ov2680 1-0036':0 [fmt:SBGGR10_1X10/800x600 field:none]"
+   media-ctl -V "'csi_mux':1 [fmt:SBGGR10_1X10/800x600 field:none]"
+   media-ctl -V "'csi_mux':2 [fmt:SBGGR10_1X10/800x600 field:none]"
+   media-ctl -V "'imx7-mipi-csis.0':0 [fmt:SBGGR10_1X10/800x600 field:none]"
+   media-ctl -V "'csi':0 [fmt:SBGGR10_1X10/800x600 field:none]"
+
+After this streaming can start. The v4l2-ctl tool can be used to select any of
+the resolutions supported by the sensor.
+
+.. code-block:: none
+    root@imx7s-warp:~# media-ctl -p
+    Media controller API version 4.17.0
+
+    Media device information
+    ------------------------
+    driver          imx-media
+    model           imx-media
+    serial
+    bus info
+    hw revision     0x0
+    driver version  4.17.0
+
+    Device topology
+    - entity 1: csi (2 pads, 2 links)
+		type V4L2 subdev subtype Unknown flags 0
+		device node name /dev/v4l-subdev0
+	    pad0: Sink
+		    [fmt:SBGGR10_1X10/800x600 field:none]
+		    <- "csi_mux":2 [ENABLED]
+	    pad1: Source
+		    [fmt:SBGGR10_1X10/800x600 field:none]
+		    -> "csi capture":0 [ENABLED]
+
+    - entity 4: csi capture (1 pad, 1 link)
+		type Node subtype V4L flags 0
+		device node name /dev/video0
+	    pad0: Sink
+		    <- "csi":1 [ENABLED]
+
+    - entity 10: csi_mux (3 pads, 2 links)
+		type V4L2 subdev subtype Unknown flags 0
+		device node name /dev/v4l-subdev1
+	    pad0: Sink
+		    [fmt:unknown/0x0]
+	    pad1: Sink
+		    [fmt:unknown/800x600 field:none]
+		    <- "imx7-mipi-csis.0":1 [ENABLED]
+	    pad2: Source
+		    [fmt:unknown/800x600 field:none]
+		    -> "csi":0 [ENABLED]
+
+    - entity 14: imx7-mipi-csis.0 (2 pads, 2 links)
+		type V4L2 subdev subtype Unknown flags 0
+		device node name /dev/v4l-subdev2
+	    pad0: Sink
+		    [fmt:SBGGR10_1X10/800x600 field:none]
+		    <- "ov2680 1-0036":0 [ENABLED]
+	    pad1: Source
+		    [fmt:SBGGR10_1X10/800x600 field:none]
+		    -> "csi_mux":1 [ENABLED]
+
+    - entity 17: ov2680 1-0036 (1 pad, 1 link)
+		type V4L2 subdev subtype Sensor flags 0
+		device node name /dev/v4l-subdev3
+	    pad0: Source
+		    [fmt:SBGGR10_1X10/800x600 field:none]
+		    -> "imx7-mipi-csis.0":0 [ENABLED]
+
+
+References
+----------
+
+.. [#f1] https://www.nxp.com/docs/en/reference-manual/IMX7SRM.pdf

Documentation/media/v4l-drivers/index.rst

@@ -44,6 +44,7 @@ For more details see the file COPYING in the source distribution of Linux.
 	davinci-vpbe
 	fimc
 	imx
+	imx7
 	ipu3
 	ivtv
 	max2175