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

Marcel Holtmann
2016-08-18T11:49:50Z

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