Re: adding can4linux to drivers/char

[Oliver Hartkopp <socketcan@hartkopp.net>]

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On 21.09.2013 01:03, Heinz-Jürgen Oertel wrote:
> Hello Linux CAN community,
> 
> long before SocketCAN, which now is part of the Linux kernel drivers, can4linux was available as the CAN device driver for Linux.
> 
> I now like to add it to the kernel source tree as well. What to you think about it. And how should I start and proceed?
> I would like to start with the Xilinx XCANPS as can be found on the Zynq processor. Maybe also with one PCI board, the CPC-PCI (EMS Wünsche).
> 
> What is the best way? My current development for the PC is based on OpenSuse with kernel 3.7.10. for Xilinx it is kernel 3.10. Can I send a patch against 3.7 and to whom can I send it?

Hello Heinz,

merging the two different approaches makes sense in that way that the
different users of the can4linux character device API should be able to take
part of the Linux mainline improvements.

The question is how to make it a win-win for both sides without doing double work:

1. SocketCAN & can4linux users should be able to use a common CAN driver pool
2. The netdev and the chardev should be able to run simultaneously
3. The chardev API preferably should support all chardev flavours

Indeed i did some evaluations about the migration from the chardev API of
can4linux to SocketCAN in my thesis on page 156ff

(unfortunately in german)
A.8 Migration existierender CAN Anwendungen

You might get the thesis from here:
http://edoc.bibliothek.uni-halle.de/servlets/DocumentServlet?id=9738

In chapter 8.2 there's a concept describing the co-existence of a character
device emulator and how to connect it to the existing Linux CAN
infrastructure. A screenshot from that picture is attached to this mail.

The advantages of this approach:

- only one hardware driver pool to maintain (e.g. add Xilinx as netdev driver)
- SocketCAN and can4linux apps can run simultaneously on the same CAN hardware
- SocketCAN protocols CAN_BCM and the CAN gateway CAN_GW are still operational
- a compact and easy maintainable chardev API adapter emulation
- can4linux API users get access to all existing CAN netdev drivers (USB, ...)

A real good thing would be if the chardev emulation adapter would support
different chardev flavours like can4linux, PEAK, LinCAN, ...

Of course there would be something to do for the existing infrastructure too.

E.g. the netlink configuration interface for the bitrate settings has to be
made accessible for the chardev emulator. Probably features of the chardev
concepts have to be integrated into the mainline CAN driver infrastruture.
Thinking about hardware filters: These can be easily emulated by the SocketCAN
filter lists, that are per-socket anyway (see picture).

Any thoughts about this idea?

Regards,
Oliver


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