From: Wolfgang Grandegger <wg-5Yr1BZd7O62+XT7JhA+gdA@public•gmane.org>
To: Arnd Bergmann <arnd-r2nGTMty4D4@public•gmane.org>
Cc: sachi-EvXpCiN+lbve9wHmmfpqLFaTQe2KTcn/@public.gmane.org,
davinci-linux-open-source-VycZQUHpC/PFrsHnngEfi1aTQe2KTcn/@public.gmane.org,
Subhasish Ghosh
<subhasish-EvXpCiN+lbve9wHmmfpqLFaTQe2KTcn/@public.gmane.org>,
nsekhar-l0cyMroinI0@public•gmane.org,
open list <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public•gmane.org>,
CAN NETWORK DRIVERS
<socketcan-core-0fE9KPoRgkgATYTw5x5z8w@public•gmane.org>,
Marc Kleine-Budde <mkl-bIcnvbaLZ9MEGnE8C9+IrQ@public•gmane.org>,
Netdev-u79uwXL29TY76Z2rM5mHXA@public•gmane.org,
m-watkins-l0cyMroinI0@public•gmane.org,
linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public•gmane.org
Subject: Re: [PATCH v4 1/1] can: add pruss CAN driver.
Date: Wed, 04 May 2011 18:00:49 +0200 [thread overview]
Message-ID: <4DC17831.3070801@grandegger.com> (raw)
In-Reply-To: <201105041648.37199.arnd-r2nGTMty4D4@public.gmane.org>
On 05/04/2011 04:48 PM, Arnd Bergmann wrote:
> On Wednesday 04 May 2011, Wolfgang Grandegger wrote:
>> On 05/04/2011 03:11 PM, Arnd Bergmann wrote:
>
>>> Wolfgang, I'm a bit worried by the API being split between sockets and sysfs.
>>> The problem is that once the sysfs API is established, users will start
>>> relying on it, and you can no longer migrate away from it, even when
>>> a later version of the Socket CAN also supports setting through a different
>>> interface. What is the current interface to set mail box IDs in software?
>>
>> Note that this CAN controller is *very* special. It cannot handle all
>> CAN id's due to a lack or resources. The PRUSS firmware is able to
>> manage just up to 8 different CAN identifiers out of the usual 4096
>> (12-bit) or even more for the extended CAN ids using 29 bits.
>
> So for other controllers, they can simply access every ID within
> the range (12 or 29 bits), but there is no need to configure?
Yes, 11 or 29 bits, to be correct.
> What are these IDs for? Do they identify a local port, a remote address,
> a connection, or something else?
It's a message identifier, which is used for bus arbitration and which
other CAN nodes can listen to. See also:
http://lxr.linux.no/#linux+v2.6.38/Documentation/networking/can.txt#L146
http://en.wikipedia.org/wiki/Controller_area_network
>> There is
>> no other CAN controller with such rather serious limitations and
>> therefore there exists also no appropriate interface. I think using
>> sysfs is OK for such device-specific parameters, at least for the time
>> being.
>
> It sounds like it's not very scalable, especially since the implementation
> is done completely in firmware. Imagine a new firmware version suddenly
> supporting 256 ids instead of 8 -- you'd then have to create 256 sysfs
> files to be compatible if I understand you correctly.
Well, than an array of CAN identifiers per file would indeed be more
appropriate.
>>> How hard would it be to implement that feature in Socket CAN?
>>
>> CAN controllers usually provide some kind of hardware CAN id filtering,
>> but in a very hardware dependent way. A generic interface may be able to
>> handle the PRUSS restrictions as well. CAN devices are usually
>> configured through the netlink interface. e.g.
>>
>> $ ip link set can0 up type can bitrate 125000
>>
>> and such a common interface would be netlink based as well.
>
> Agreed.
>
>>> Is that something that Subhasish or someone else could to as a prerequisite
>>> to merging the driver?
>>
>> Any ideas on how to handle hardware filtering in a generic way are
>> welcome. I will try to come up with a proposal sooner than later.
>
> It sounds to me like the best solution would be change the firmware
> to lift that restriction and simply allow all IDs, in case it's not
> actually a hardware limitation (which sounds unlikely).
Yes, that would be best but they told us, that it's not possible with
the available hardware resources. Subhasish?
> If that's not possible, maybe it's possible to define a generic
> filtering interface using netlink, and then either do it completely
> in the kernel, or using the hardware support.
Well, I hesitate to implement an interface especially for such an exotic
device. Fine if it could be handled by a generic CAN hardware filter
interface, which is especially useful for normal CAN controllers.
Wolfgang.
next prev parent reply other threads:[~2011-05-04 16:00 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1303474267-6344-1-git-send-email-subhasish@mistralsolutions.com>
2011-04-22 12:11 ` [PATCH v4 1/1] can: add pruss CAN driver Subhasish Ghosh
[not found] ` <1303474267-6344-2-git-send-email-subhasish-EvXpCiN+lbve9wHmmfpqLFaTQe2KTcn/@public.gmane.org>
2011-04-22 15:50 ` Marc Kleine-Budde
[not found] ` <4DB1A3B7.7060300-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
2011-04-25 20:06 ` Wolfgang Grandegger
[not found] ` <4DB5D452.9050500-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2011-04-27 13:08 ` Subhasish Ghosh
2011-04-27 13:21 ` Marc Kleine-Budde
2011-04-27 13:25 ` Arnd Bergmann
[not found] ` <201104271525.28512.arnd-r2nGTMty4D4@public.gmane.org>
2011-05-04 7:13 ` Subhasish Ghosh
2011-05-04 13:11 ` Arnd Bergmann
[not found] ` <201105041511.54095.arnd-r2nGTMty4D4@public.gmane.org>
2011-05-04 14:33 ` Wolfgang Grandegger
[not found] ` <4DC163D7.9010309-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2011-05-04 14:48 ` Arnd Bergmann
[not found] ` <201105041648.37199.arnd-r2nGTMty4D4@public.gmane.org>
2011-05-04 16:00 ` Wolfgang Grandegger [this message]
[not found] ` <4DC17831.3070801-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2011-05-10 10:11 ` Subhasish Ghosh
2011-05-10 10:27 ` Alan Cox
[not found] ` <20110510112734.54160824-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org>
2011-05-10 12:21 ` Subhasish Ghosh
2011-05-11 21:31 ` Arnd Bergmann
[not found] ` <201105112331.47954.arnd-r2nGTMty4D4@public.gmane.org>
2011-05-11 21:44 ` Arnd Bergmann
[not found] ` <201105112344.44171.arnd-r2nGTMty4D4@public.gmane.org>
2011-05-11 22:39 ` Marc Kleine-Budde
2011-05-11 22:56 ` Alan Cox
[not found] ` <20110511235652.7ccddb3b-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org>
2011-05-12 3:03 ` can: hardware vs. software filter Kurt Van Dijck
2011-05-12 7:13 ` [PATCH v4 1/1] can: add pruss CAN driver Wolfgang Grandegger
[not found] ` <4DCB88A4.2010901-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2011-05-12 10:58 ` Kurt Van Dijck
2011-05-12 12:54 ` Arnd Bergmann
[not found] ` <201105121454.47781.arnd-r2nGTMty4D4@public.gmane.org>
2011-05-12 13:04 ` Marc Kleine-Budde
2011-05-12 14:41 ` Oliver Hartkopp
[not found] ` <4DCBF1B6.6000104-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
2011-05-22 10:30 ` Arnd Bergmann
[not found] ` <201105221230.56243.arnd-r2nGTMty4D4@public.gmane.org>
2011-05-23 6:21 ` Oliver Hartkopp
[not found] ` <4DD9FCFC.10803-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
2011-05-23 8:23 ` Marc Kleine-Budde
2011-05-27 8:31 ` Wolfgang Grandegger
2011-05-12 7:04 ` Wolfgang Grandegger
2011-05-04 15:57 ` Kurt Van Dijck
2011-05-04 16:09 ` Wolfgang Grandegger
[not found] ` <4DC17A31.8070409@grandegger.com>
[not found] ` <4DC17A31.8070409-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2011-05-04 20:55 ` Oliver Hartkopp
2011-04-27 13:28 ` Wolfgang Grandegger
[not found] ` <4DB81A12.1000006-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2011-04-27 13:34 ` Wolfgang Grandegger
2011-04-24 11:13 ` Marc Kleine-Budde
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