linux-kernel - Re: [RFC PATCH 0/3] UART slave device bus

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Date:   Mon, 22 Aug 2016 18:02:54 +0100
From:   One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:     Rob Herring <robh@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        Jiri Slaby <jslaby@...e.com>,
        Sebastian Reichel <sre@...nel.org>,
        Pavel Machek <pavel@....cz>,
        Peter Hurley <peter@...leysoftware.com>,
        NeilBrown <neil@...wn.name>,
        "Dr . H . Nikolaus Schaller" <hns@...delico.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        "open list:BLUETOOTH DRIVERS" <linux-bluetooth@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/3] UART slave device bus

> > I think there are two other valuable features provided by serio:
> >
> > - an existing set of drivers written to the API
> > - the implementation of the tty_ldisc  
> 
> True, though I'd expect little of the data flow part of it to be reused.

Then your design is broken.

> - a child of the uart node
> - a reg property containing the line number if the parent has multiple
> uarts (I'd expect this to rarely be used).

That surprises me as for current x86 platforms it would be the norm,
except that we use ACPI.

> - baudrate and other line configuration (though I would expect the
> slave driver to know all this and set it w/o DT. Also, we already have
> a way to set baudrate in the parent node at least.)
> - other standard device properties for interrupt, gpios, regulators.
> 
> Also to consider is whether muxing of multiple slaves is needed. It's
> not anything I've seen come up, but it's not hard to imagine. I think
> that can be considered later and shouldn't impact the initial binding
> or infrastructure.

You can describe the child of the serial device as a mux and the children
of the mux as whatever so it comes out fine when you get to that point.

Alan