> Would it make sense then to define a DT binding that can cover these
> four cases independent of the Linux usage:
>
> a) an existing tty line discipline matched to a tty port
> b) a serio device using the N_MOUSE line discipline (which
> happens to cover non-mouse devices these days)
These two are the same basic thing
port x expects ldisc y {with properties ...}
> c) a uart_port slave attached directly to the uart (like in your
> current code)
c) needs to be a tty_port slave attached directly to a tty_port.
Important detail, but as uart_port is just a subset of tty_port it's a
trivial detail to the DT.
> d) the same slave drivers using a new tty line discipline
and this is also just a/b again.
What use cases and connectivity do you need to describe. Looking at the
ACPI platforms we have
- the expected serial port configuration
- the properties of the port (FIFO etc)
- the power management for the port
- the children of the port
- the power management of the children (at a very simplistic abstracted
level)
So we want to be able to describe something like
ttyS0 {
baud: 1152008N1
protocol: bluetooth hci
fixed: yes
powermanagement: { ... }
}
and if I look at the usermode crapfest on a lot of Android systems it
looks similar but with the notion of things like being able to describe
- Use GPIO mode sleeping and assume first char is X to save power
- Power up, wait n ms, write, read, wait n ms, power down (which
has to be driven at the ldisc/user level as only the ldisc
understands transactions, or via ioctls (right now Android user
space tends to do hardcoded writes to /sys.. gpio to drive power
- And a few variants thereof (power up on write, off on a timer
etc)
So I can imagine wanting to describe something like
- The bluetooth HCI hardware is managed by gpio 11 (or UART DTR,
or PMIC n etc)
The uart can switch into GPIO mode and is gpio 15
or
- Raise gpio 4 when writing, drop it after 50mS with no read/write
Then the ldisc needs to make port->ops. calls for enabling/disabling low
power mode and expected char, and the uarts that can do it need to
implement the gpio/uart switching and any timers.
Alan
