Option to disable setting readback?

[ShaneMurphy2]

Some background, I'm working with a Xilinx UARTLite IP. This serial device is very barebones, and doesn't support all features. As such, the driver handles calls to tcsetattr a little oddly, in that it will mutate the settings the user passed in to be what the device supports. This causes an issue with opening this port using this library, since it calls tcgetattr after tcsetattr. For some combinations of settings, the readback will be different. For this device, that is not a problem. The core, low-level settings are configured in hardware (data bits, flow control, etc.).

The only thing I need this library to do is higher level setup. I recognize I can construct a TTYPort instance from a raw FD, but I was having difficulty getting that to work reliably when constructing a SerialStream from tokio_serial.

My proposal is to add a setting to the builder called best_effort, that when passed true will disable the call to tcgetattr and the setting check. So, my question is: is this use case of a devious device driver is common enough to warrant an upstream change like this?

[sirhcel]

Hello @ShaneMurphy2, you are not alone experiencing such behavior. I've seen this for CRTSCTS the flag in Fazecast/jSerialComm#453 (comment). Apparently few people are actually hitting such issues.

What is the actual show stopper for you in your case? Getting an error from SerialPortBuilder::open?

Interestingly, reading back termios flags only seems to happen SerialPortBuilder::open and not in other functions changing them.

[ShaneMurphy2]

Yeah, it was opening the port. I got around it by writing my own version of open that steals borrows from serialport and uses a fork of tokio-serial that allows constructing a SerialStream from a raw TTYPort. The version I wrote takes the same settings as SerialPortBuilder, but uses them as a sanity check, but does not try to apply them since my particular port is not configurable.