On Mon, Jun 12, 2017 at 01:17:18PM +0300, Tal Shorer wrote: > On Mon, Jun 12, 2017 at 9:48 AM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > 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 > > I'm not sure what you mean by "loopback", but if you mean an > application that poll()s the two sides, reads from one side and writes > to the other, I'm already doing that. My issue is that: > 1. f_acm doesn't do anything with set_line_coding. > 2. even if it did, the tty core has no easy way to notify the user of that. Ah, I understand now, thanks. Yeah, that's a problem :) 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
