Line discipline

[Okash Khawaja]

On Mon, Nov 21, 2016 at 10:36 PM, Samuel Thibault <
samuel.thibault at ens-lyon.org> wrote:

> Hello,
>
> Okash Khawaja, on Mon 21 Nov 2016 22:32:52 +0000, wrote:
> > 1. register ldisc structure in spk_tty_probe().
>
> Registering the speakup line discipline should be done on speakup module
> insertion (speakup_init), since we're supposed to do it just once.
>
> > 2. in spk_tty_probe(), attach line discipline - like you would for
> /dev/ttyX
> > from user space
>
> spk_tty_probe also needs to open ttySX itsef.
>
> > 3. in open() method of ldisc structure, take the tty_struct and cache it.
>
> Yes.
>
> > 4. in spk_serial_out_tty() call tty->ops->write() instead of outb().
>
> Yes.
>
> Samuel
>

Thanks.

So I have a simple kernel module that registers a new ldisc. When userspace
attaches that ldisc to /dev/ttyS0, the kernel module is able to write to
that serial port using tty->ops->write().

Currently I'm investigating the core problem of opening /dev/ttyS0 from
kernel space and attaching our ldisc to it. Are there any existing ideas
around this? Is this worth investigating: to find correct tty without
opening /dev/ttyS0 and assigning our ldisc to it. Realistically, how early
in boot process do we want the ldisc assigned?