Likely an issue w/ macOS + ARM + USB/C

[kanalo-shrek]

Hi 👋 , Happy Holidays and thanks for the incredible work on ddc-macos-rs!

I'm encountering reliability issues with DDC/CI communication when using DisplayPort over USB-C connection. Initially using ddc-hi (which uses this package), I ran into several issues that I've partially resolved but still need help addressing.

Environment

• OS: macOS
• Display Connection: DisplayPort over USB-C
• Package: Using ddc-hi which depends on macOS-ddc-rs

Initial Problems

1. Getting DDC/CI error: invalid DDC/CI length error
2. get_vcp_feature fails with the same error
3. set_vcp_feature appears to succeed but has no effect on the monitor

Investigation

I compared the implementation with m1ddc which works well with my setup. The main difference I noticed was in m1ddc the write command section waits and invokes IOAVServiceWriteI2C multiple times for DDC_ITERATIONS:
Reference in m1ddc

Current Implementation

I've tried to match m1ddc's approach and tweaked the rust code for execute to:

unsafe {
    for _ in 0..DDC_ITERATIONS {
        std::thread::sleep(response_delay);
        verify_io(IOAVServiceWriteI2C(
            *service,
            i2c_address as _, // I2C_ADDRESS_DDC_CI as u32,
            SUB_ADDRESS_DDC_CI as _,
            // Skip the first byte, which is the I2C address, which this API does not need
            request_data[1..].as_ptr() as _,
            (request_data.len() - 1) as _, // command_length as u32 + 3,
        ))?;    
    }
};

Current Status

• The above changes resolved the initial errors
• Commands now execute without errors
• I am not sure if why this works!

Questions

1. Are there known issues with monitor detection over USB-C DisplayPort?
2. Is there some obvious configuration that I am missing?

Additional Context

I'd be happy to help investigate further or implement suggested changes. Please let me know what additional information would be helpful.