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Subject: Re: [RFC PATCH 0/3] UART slave device bus
From: "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <20160818111046.GE7427@amd>
Date: Thu, 18 Aug 2016 13:18:25 +0200
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Marcel Holtmann <marcel@holtmann.org>, Rob Herring <robh@kernel.org>,
        Jiri Slaby <jslaby@suse.com>, Sebastian Reichel <sre@kernel.org>,
        Peter Hurley <peter@hurleysoftware.com>, NeilBrown <neil@brown.name>,
        Arnd Bergmann <arnd@arndb.de>,
        Linus Walleij <linus.walleij@linaro.org>,
        linux-bluetooth@vger.kernel.org, linux-serial@vger.kernel.org,
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To: Pavel Machek <pavel@ucw.cz>
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> Am 18.08.2016 um 13:10 schrieb Pavel Machek <pavel@ucw.cz>:
> 
> Hi!
> 
>>> I am actually not convinced that GPS should be represented as
>>> /dev/ttyS0 or similar TTY. It think they deserve their own driver
>>> exposing them as simple character devices. That way we can have a
>>> proper DEVTYPE and userspace can find them correctly. We can also
>>> annotate them if needed for special settings.
>> 
>> I would _love_ to see that happen, but what about the GPS line
>> discipline that we have today?  How would that match up with a char
>> device driver?
> 
> ./drivers/usb/serial/garmin_gps.c ?
> 
> Hmm, some cleanups would be welcome there... plus it would be good to
> know what is its interface to userland... it is not easily apparent
> from the code.
> 
> Actually, having some kind of common support for GPSes in the kernel
> would be nice. (Chardev that spits NMEA data?

Yes and no. How do you apply tcsetattr to such a device? More or less
by implementing another tty stack?

> ) For example N900 GPS is
> connected over network (phonet) interface, with userland driver
> translating custom protocol into NMEA. Not very nice from "kernel
> should provide hardware abstraction" point of view.

Indeed. In such a case the translation should be done in the kernel.
But it is not necessary for devices that already provide NEMA over UART.
Still user-space should be able to tcsetattr how it wants to see the records
(mainly CR/LF translations).

BR,
Nikolaus