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

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Message-Id: <951C95FD-35DD-4EC5-A62C-31378B85EF14@holtmann.org>
Date:	Thu, 18 Aug 2016 13:49:45 +0200
From:	Marcel Holtmann <marcel@...tmann.org>
To:	"H. Nikolaus Schaller" <hns@...delico.com>
Cc:	Pavel Machek <pavel@....cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rob Herring <robh@...nel.org>, Jiri Slaby <jslaby@...e.com>,
	Sebastian Reichel <sre@...nel.org>,
	Peter Hurley <peter@...leysoftware.com>,
	NeilBrown <neil@...wn.name>, Arnd Bergmann <arnd@...db.de>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-bluetooth@...r.kernel.org, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, herkne@....de
Subject: Re: [RFC PATCH 0/3] UART slave device bus

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