7.2. Amlogic C3 Image Signal Processing (C3ISP) driver — The Linux Kernel documentation

# 7.2. Amlogic C3 Image Signal Processing (C3ISP) driver

## 7.2.1. Introduction

This file documents the Amlogic C3ISP driver located under drivers/media/platform/amlogic/c3/isp.

The current version of the driver supports the C3ISP found on Amlogic C308L processor.

The driver implements V4L2, Media controller and V4L2 subdev interfaces. Camera sensor using V4L2 subdev interface in the kernel is supported.

The driver has been tested on AW419-C308L-Socket platform.

## 7.2.2. Amlogic C3 ISP

The Camera hardware found on C308L processors and supported by the driver consists of:

- 1 MIPI-CSI-2 module: handles the physical layer of the MIPI CSI-2 receiver and receives data from the connected camera sensor.

- 1 MIPI-ADAPTER module: organizes MIPI data to meet ISP input requirements and send MIPI data to ISP.

- 1 ISP (Image Signal Processing) module: contains a pipeline of image processing hardware blocks. The ISP pipeline contains three resizers at the end each of them connected to a DMA interface which writes the output data to memory.

A high-level functional view of the C3 ISP is presented below.:

                                                                     +----------+    +-------+
                                                                     | Resizer  |--->| WRMIF |
    +---------+    +------------+    +--------------+    +-------+   |----------+    +-------+
    | Sensor  |--->| MIPI CSI-2 |--->| MIPI ADAPTER |--->|  ISP  |---|----------+    +-------+
    +---------+    +------------+    +--------------+    +-------+   | Resizer  |--->| WRMIF |
                                                                     +----------+    +-------+
                                                                     |----------+    +-------+
                                                                     | Resizer  |--->| WRMIF |
                                                                     +----------+    +-------+

## 7.2.3. Driver architecture and design

With the goal to model the hardware links between the modules and to expose a clean, logical and usable interface, the driver registers the following V4L2 sub-devices:

- 1 c3-mipi-csi2 sub-device - the MIPI CSI-2 receiver

- 1 c3-mipi-adapter sub-device - the MIPI adapter

- 1 c3-isp-core sub-device - the ISP core

- 3 c3-isp-resizer sub-devices - the ISP resizers

The c3-isp-core sub-device is linked to 2 video device nodes for statistics capture and parameters programming:

- the c3-isp-stats capture video device node for statistics capture

- the c3-isp-params output video device for parameters programming

Each c3-isp-resizer sub-device is linked to a capture video device node where frames are captured from:

- c3-isp-resizer0 is linked to the c3-isp-cap0 capture video device

- c3-isp-resizer1 is linked to the c3-isp-cap1 capture video device

- c3-isp-resizer2 is linked to the c3-isp-cap2 capture video device

The media controller pipeline graph is as follows (with connected a IMX290 camera sensor):

Media pipeline topology

## 7.2.4. Implementation

Runtime configuration of the ISP hardware is performed on the c3-isp-params video device node using the V4L2_META_FMT_C3ISP_PARAMS as data format. The buffer structure is defined by `c3_isp_params_cfg`.

Statistics are captured from the c3-isp-stats video device node using the V4L2_META_FMT_C3ISP_STATS data format.

The final picture size and format is configured using the V4L2 video capture interface on the c3-isp-cap[0, 2] video device nodes.

The Amlogic C3 ISP is supported by libcamera with a dedicated pipeline handler and algorithms that perform run-time image correction and enhancement.