[FAQ] What are the common reasons a CSI sensor fails to probe in V4L2 environment?

There can be various reasons why a sensor doesn't probe. Here are a few things to check and debug.

1. Check the boot message and see if the CSI2-Rx interface is probed.

Run the following command:

 root@am62axx-evm:~# dmesg | grep csi

If this command returns nothing, it most likely means that device tree overlay for the sensor is not loaded. Then check the u-boot message for any dtbo load failure, for example

Working FDT set to 88000000
Failed to load '/boot/dtb/k3-am62x-sk-csi2-imx219.dtbo'

The above message indicates that the dtbo file can not be found and loaded. The path should be "/boot/dtb/ti/<sensor dtbo file>". The solution is to add "ti/" in the dtbo path:

name_overlays=ti/<sensor dtbo file>

If the "dmesg | grep csi" command shows probe failure, such as below, it is most likely caused by errors in the device tree overlay for CSI2-RX.

cdns-csi2rx: probe of 30101000.csi-bridge failed with error -22

Check the device tree overlay of the sensor by comparing to the existing sensor overlays in the SDK. One common error is using the wrong CSI-2 Rx port. For example, AM62A SoC has only one CSI-2 Rx port and "csi0_port0" should be used as below in the IMX219 overlay:

&csi0_port0 {
	status = "okay";

	csi2rx0_in_sensor: endpoint {
		remote-endpoint = <&csi2_cam0>;
		bus-type = <4>; /* CSI2 DPHY. */
		clock-lanes = <0>;
		data-lanes = <1 2>;
	};
};

If the device tree overlay for CSI2-Rx interface is correct, it should have the following message:

root@am62axx-evm:~# dmesg | grep csi
cdns-csi2rx 30101000.csi-bridge: Probed CSI2RX with 2/4 lanes, 4 streams, external D-PHY

2. Check the boot message and search for sensor probing errors.

For example, one common sensor probing error is:

root@am62axx-evm:~# dmesg | grep imx219
[    6.520787] imx219 4-0010: Error reading reg 0x0000: -121
[    6.520796] imx219 4-0010: failed to read chip id 219
[    6.547515] imx219: probe of 4-0010 failed with error -121

If this kind of error is seen, try the following debug options:

• Check camera connection. If the 22-pin/15-pin FFC connector is used, make sure the pins are properly aligned. 
• Check the board schematics and make sure the right I2C bus is used in the sensor's device tree overlay. Make sure the right I2C address for the sensor is used in the overlay.
• Run "i2cdetect" on the I2C bus that the camera is connected to and check if the sensor I2C address can be seen. For example, on AM62A Starter Kit, the CSI camera is using the SoC I2C 2 mux (switch) channel 1. Below i2cdetect commands show that a device at address 0x10 (IMX219) on i2c-2-mux (chan_id 1) is detected:
  

  root@am62axx-evm:~# i2cdetect -l
  i2c-0   i2c             OMAP I2C adapter                        I2C adapter
  i2c-1   i2c             OMAP I2C adapter                        I2C adapter
  i2c-2   i2c             OMAP I2C adapter                        I2C adapter
  i2c-3   i2c             i2c-2-mux (chan_id 0)                   I2C adapter
  i2c-4   i2c             i2c-2-mux (chan_id 1)                   I2C adapter
  i2c-5   i2c             i2c-1-mux (chan_id 0)                   I2C adapter
  
  root@am62axx-evm:~# i2cdetect -y -r 4
       0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
  00:                         -- -- -- -- -- -- -- --
  10: UU -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
  20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
  30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
  40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
  50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
  60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
  70: -- UU -- -- -- -- -- --

For other common problems related to CSI camera please refer to this FAQ:

• [FAQ] Most common problems encountered when developing camera applications on the AM6x