On Fri, Jul 07, 2023 at 04:37:53PM +0530, Ayush Singh wrote:
Hello everyone, I am working on a Google Summer of Code 2023 project [1] under BeagleBoard.or. In this project, I have to write a Linux driver that exposes `dev/ttyMCU0` (or something else) which can be accessed as a Serial tty by MCUmgr [2]. This then sends the data and gets the response from the CC1352 processor in BeagelPlay [3], which runs Zephyr over HDLC UART (the data for this tty port has a particular HDLC address).
However, all the resources I could find seem to use deprecated or old APIs (like `alloc_tty_driver` instead of `tty_alloc_driver`). After some trial and error, I was able to transfer the data written to `ttyMCU0` to CC1352 using `write` in `tty_operations`. However, I am stumped on how to send data to tty from the driver so that the userspace application can read it (like using `cat`). Supposedly it should be done using `tty_insert_flip_char` but the signature for this function in the tutorials and the one present at `tty_flip.h` is quite different and does not seem to work for me. Also, there seems to be something about the Echo flag but not sure what all that is.
Finally, I am not sure I understand the relationship between tty port, tty device, and tty driver either so it would be great if someone can guide me to resources related to tty. I think a simple tty echo driver should allow me to get the hang of what I am supposed to do.
Try looking at the tty driver example in the book, "Linux Device Drivers, third edition". It's out of date, but the ideas a much the same in places for tty drivers. And then look at any of the hundreds of in-kernel tty drivers for examples of what to do. You might want to look at the "smaller" ones as you don't want to get bogged down with the uart-specific stuff. good luck! greg k-h