Linux I2C Driver unable to read register in adt7420

[jmacagba]

In both linux_i2c_read and linux_i2c_write, the stop_bit condition is ignored;

• However, as per my understanding, this is crucial for I2C communication, since we might need a repeated start condition on certain use cases.

The error I have encountered is when reading a register for adt7420 which is always 0.

• From what I understand,
  • LOC 453 will write the register address (that needs to be read) and a stop_bit should not be generated (However, when using Linux Platform, stop_bit does not do anything)
  • LOC 456, will read back the register value and a stop_bit should be generated (However, when using Linux Platform, stop_bit does not do anything)
• I think the issue is with using write() and read() for I2C, which cannot use/implement stop_bit (where in each write/read might automatically send a stop_bit)
  • Note: I was able to replicate this issue in a simple C Program
• Instead, I have found that using ioctl(file,I2C_RDWR, &packets); or __s32 i2c_smbus_read_byte_data(int file, __u8 command); are working alternatives
  • Note: I was only able to test this in a simple C program and have not tested it on the Linux I2C Driver.
  • Reference: Implementing I2C device drivers in userspace — The Linux Kernel documentation

[buha]

Hi, I checked the current implementation of our I2C API for the linux userspace platform, and indeed, the stop_bit is ignored.

https://github.com/analogdevicesinc/no-OS/blob/main/drivers/platform/linux/linux_i2c.c#L160

This is definitely something that needs to be fixed, we will do it but I can't offer a timeline right now. If you would like to contribute and make a pull request that would be awesome!