Re: adding can4linux to drivers/char

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 09/29/2013 07:45 PM, Sebastian Haas wrote:
> I think Heinz-Jürgens' arguments are not that wrong. There are a bunch
> of example in the kernel of concurring solution for the same issues
> every single one with different advantages and disadvantages (just
> compare how many solution for virtualization are available kvm, xen,
> paravirt, ...).

You're right.

> There must be space in kernel for the classical chardev CAN-approach.
> Sharing common code to access the different controllers must be
> possible.

That's already implemented in the Kernel, it's called a driver.

> I think there are a bunch of use cases out there which are easier and
> more efficiently solved with a simple chardev API. A simple chardev
> CAN driver like can4linux provide doesn't depend on the whole
> networking subsystem which may be imported of real embedded systems
> with strong memory constraints (less memory footprint, smaller
> kernel).

The smallest system we're running Linux is a Cortex M3, it's on chip RAM
is to small for Kernel + Userspace, so you need an external RAM chip
anyways.

> The Socket approach has some real advantages (multi-user for single
> CAN controller, iptables filtering, netutil integration, buffering,
> ..), but many of them may be considered as disadvantages as well (no
> control of the message flow in terms of timing and ordering, no

You you have ordering problem? That's a bug? Which driver/hardware?

> exclusive use of the interface, networking dependency). Implementing
> an automatic bitrate detection or application driver busoff recovery
> is a pain in the ass with SocketCAN.

If there is a need for bitrate detection, feel free request it here. I
think there are some controllers that support this in hardware, while
others don't. Is there a known working algorithm for bitrate detection?
How can we make busoff recovery better? What's the most annoying point?

Marc
-- 
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