Can't use ioctl() to control a device owned by kernel module?

OliverChen · 08-07-2019, 10:21 PM

Hi!

I failed to use C/C++ to access the image sensor OV5645's register on my system via I2C bus. Below are some information about my system:

Hardware:
Dragonboard 410c +
96Boards MIPI Adapter with Dual OV5645
(https://www.ebay.com/itm/96Boards-MI...525BC%25252589)
OS :
Linaro Linux (Debian based) 19.01

As I can use GStreamer to control the two OV5645 to feedback captured images, the hardware connections seems to be fine. Below are some information about the I2C master and OV5645 in my system:

Code:

    linaro@linaro-developer:~$ sudo i2cdetect -l
    i2c-3   i2c             QUP I2C adapter                         I2C adapter
    i2c-1   i2c             QUP I2C adapter                         I2C adapter
    i2c-4   i2c             Qualcomm Camera Control Interface       I2C adapter
    i2c-0   i2c             QUP I2C adapter                         I2C adapter

    linaro@linaro-developer:~$ dmesg | grep ov5645
    [   11.825197] ov5645 4-003b: OV5645 detected at address 0x3b
    [   12.290626] ov5645 4-003a: OV5645 detected at address 0x3a

And here is my short program: https://gist.github.com/oliverjungen...7e7a3c0678c41e

What it does are simply:

1. Open /dev/i2c-4

Code:

file = open(filename, O_RDWR);

2. Set I2C slave address 0x3b

Code:

errno = ioctl(file, I2C_SLAVE_FORCE, CAM_REAR_I2C_ADDR);

3. Send 16-bit register address 0x300a to this I2C slave

Code:

ret = write(file, &reg, 2);

However, when it runs, I always get:

Code:

Write i2c internal address error: Input/output error

This message was printed by perror() in this program’s Line 54, after writing the register address (0x300a, SENSOR CHIP ID HIGH BYTE) to OV5645.

I found that, when this error occurs, the kernel module i2c-qcom-cci reports error messages like:

Code:

    linaro@linaro-developer:~$ dmesg | grep cci
    [ 1280.099448] i2c-qcom-cci 1b0c000.cci: Master 0 error 0x08000000
    [ 1280.099502] i2c-qcom-cci 1b0c000.cci: master 0 queue 0 error -5
    [ 1280.104247] i2c-qcom-cci 1b0c000.cci: cci i2c xfer error -5

These I2C slaves (these OV5645) are actually owned by kernel modules. That's the reason why I use I2C_SLAVE_FORCE instead of I2C_SLAVE as the flag when I set the I2C slave address: errno = ioctl(file, I2C_SLAVE_FORCE, CAM_REAR_I2C_ADDR);

I'm wondering whether I can't use ioctl() to control a device owned by kernel modules?

smallpond · 08-08-2019, 02:27 PM

I don't think you should be opening the i2c device to talk to the camera. That bus probably is owned by the kernel i2c driver and not shared. You should be opening the ov5645 device as described here:

https://www.linuxtv.org/downloads/le...v4l2.html#open

OliverChen · 08-08-2019, 07:35 PM

Hi smallpond,
First thank you for your reply.
OK, I understand. I've found a lot of information in the Video for Linux Two API Specification I should study. Hopefully it will lead me to find the solution of this issue.
Thanks again and I wish you a good day!

OliverChen · 08-12-2019, 08:04 AM

For anyone who may concern:
The root cause of this symptom is:
OV5645’s kernel module will turn OV5645’s power off (or power-saving?) after initializing it. After turning its power on manually, now it’s OK to access OV5645’s registers.
FYR.

Hi smallpond,
Thank you for your kind help, anyway!