On Sun, Jun 11, 2017 at 11:41:02PM +0300, Tal Shorer wrote: > I'm currently working on a project where I'd like to have an omap board > running linux be a usb-to-uart converter (using f_acm). I have an > application that holds both the ttyGS* and the ttyO* port (the physical > uart port) open, polls for readable data, and writes any incoming data > to the other side. > > I'd also like the host to be able to configure baudrate, parity, etc. > My thought on how to achieve this is to modify how the ttyGS* ports > behave by adding a POLLPRI event when set_line_coding is received. In > order to do that several steps will have to be taken: > - one of: > 1. add a poll() callback to struct tty_operations and call it in > n_tty_poll(). u_serial and f_acm will implement required > callbacks to allow returning POLLPRI when necessary. > 2. add a flag to struct tty_struct that indicates an exceptional > condition and make n_tty_poll() return POLLPRI if that flag is > set. this will also require a new wait queue to allow us to wait > for such an event. > - after receiving SET_LINE_CODING (and verifying it), set whatever flag > is necessary to wake the user with POLLPRI. > - implement the ioctl() callback in u_serial and f_acm to allow the > user to get the line coding set by the host, with which it can > configure the hardware port accordingly. > > Does my approach make sense? Assuming I do that, which tree should such > a series be sent to? usb-gadget? tty? Why not just do it all in userspace, a simple "loopback" program should be able to handle this. If not, look into the 'serdev' interface now in the kernel, that might help out a lot with what you want to do here. And I really doubt you need to touch the tty core or ldisc for this, that seems a bit extreme. good luck! greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
