netdev - Re: Staging: cpc-usb CAN driver TODO list

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Date:	Mon, 07 Sep 2009 07:56:50 +0200
From:	Sebastian Haas <haas@...-wuensche.com>
To:	Oliver Hartkopp <oliver@...tkopp.net>
CC:	Greg KH <greg@...ah.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Felipe Balbi <me@...ipebalbi.com>,
	Wolfgang Grandegger <wg@...ndegger.com>
Subject: Re: Staging: cpc-usb CAN driver TODO list

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Oliver,

I'm not yet sure how to actually start the development. There is so much
to do, and I've not much time to spend on this, unfortunately. Because
of this I can't rewrite the whole driver on my own in order to get a
Socket-CAN driver but I can provide support, review patches, rent
devices and make tests here.

Oliver, you are not familiar with USB and I'm not very familiar with CAN
netdev internals, why not combining these twos. You are writing the CAN
part and write the USB part.

I'll also write a specification which contains any information you need
to develop a CAN driver for the device (commands, sequences, error
handling).

- --
Mit freundlichen Gruessen/Best Regards,

Sebastian Haas
Software Entwicklung/Software Development

Phone: +49-9451-9432-22
Fax  : +49-9451-9432-12
Email: haas@...-wuensche.com
Web  : www.ems-wuensche.com


Oliver Hartkopp schrieb:
> Hello Greg and Sebastian,
> 
> i just looked around in the linux-next tree for the cpc-usb driver.
> 
> http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git;a=tree;f=drivers/staging/cpc-usb;hb=HEAD
> 
> IMHO the sja2m16c* files are completely obsolete as the setting of the CAN
> bittimings needs to be done by separate functions (one for the SJA1000 and one
> for the M16C). For both of them a separate can_bittiming_const is needed, like
> it is defined in drivers/net/can/sja1000/sja1000.c:
> 
> static struct can_bittiming_const sja1000_bittiming_const = {
> 	.name = DRV_NAME,
> 	.tseg1_min = 1,
> 	.tseg1_max = 16,
> 	.tseg2_min = 1,
> 	.tseg2_max = 8,
> 	.sjw_max = 4,
> 	.brp_min = 1,
> 	.brp_max = 64,
> 	.brp_inc = 1,
> };
> 
> Also a separate function to determine the register values from the calculated
> bittiming values is needed for both hardware types (SJA1000(LPC2119)/M16C) of
> the cpc-usb. How this is done can be checked in linux/drivers/net/can/* or in
> the source code of upcoming drivers in
> 
> http://svn.berlios.de/svnroot/repos/socketcan/trunk/kernel/2.6/drivers/net/can/
> 
> I wondered about the following items in the TODO list:
> 
> 	- tie into CAN socket interfaces if possible
> 	- figure out sane userspace api
> 
> This is definitely a no go! IMO there is no real alternative to make this
> cpc-usb driver a real CAN network driver.
> 
> The CAN driver interface has a sane configuration API via netlink and brings
> everything to configure CAN specific bitrates, error counters, recovery, etc.
> 
> The missing thing is to connect the usb-device to a netdevice (can%d), remove
> all the chardev file-I/O stuff and adapt the cpc-usb to use the
> bitrate-settings, error counters and whatever - which is already well-defined
> and provided by the CAN driver interface library contributed by Wolfgang
> Grandegger ( drivers/net/can/dev.c and include/linux/can/[dev.h|netlink.h] ).
> 
> Unfortunately i'm not an expert in USB programming and i don't have that
> hardware - but if you need some ideas from the CAN driver peoples like
> Wolfgang, questions are always welcome, e.g. on the socketcan-core ML:
> 
> http://developer.berlios.de/projects/socketcan
> 
> I don't think it's a big effort for people that know USB & CAN to clean up the
> cpc-usb and make it a slim CAN netdev. Believe me, it took years to figure out
> a sane userspace api for CAN interfaces, which is now provided by the netlink
> interface ;-)
> 
> Best regards,
> Oliver
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