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Subject: Re: [RFC PATCH 0/3] UART slave device bus
From: Marcel Holtmann <marcel@holtmann.org>
In-Reply-To: <A8AFECE4-8501-4186-A834-5E08EEE8A0C4@goldelico.com>
Date: Thu, 18 Aug 2016 13:49:45 +0200
Cc: Pavel Machek <pavel@ucw.cz>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.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,
	linux-kernel@vger.kernel.org, herkne@gmx.de
Message-Id: <951C95FD-35DD-4EC5-A62C-31378B85EF14@holtmann.org>
References: <20160818011445.22726-1-robh@kernel.org> <118926C8-F4D0-41F5-B6A8-690E0312F3FB@goldelico.com> <28DDAF2B-2341-403B-80D8-DA0A63F51FF1@holtmann.org> <20160818105521.GB7031@kroah.com> <20160818111046.GE7427@amd> <A8AFECE4-8501-4186-A834-5E08EEE8A0C4@goldelico.com>
To: "H. Nikolaus Schaller" <hns@goldelico.com>
Sender: linux-serial-owner@vger.kernel.org
List-ID: <linux-bluetooth.vger.kernel.org>

Hi Nikolaus,

>>>> 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).

I disagree here. NMEA is a standard and the kernel should just enforce framing of NMEA sentences. It makes no difference what the CR/LF is. Userspace gets full sentences.

Regards

Marcel