Messages in this thread | | | Date | Mon, 22 Aug 2016 16:45:33 +0100 | From | One Thousand Gnomes <> | Subject | Re: [RFC PATCH 0/3] UART slave device bus |
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> 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
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