linux-kernel - Re: [PATCH v4 1/1] can: add pruss CAN driver.

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Date:	Wed, 04 May 2011 18:09:21 +0200
From:	Wolfgang Grandegger <wg@...ndegger.com>
To:	Arnd Bergmann <arnd@...db.de>,
	Subhasish Ghosh <subhasish@...tralsolutions.com>,
	linux-arm-kernel@...ts.infradead.org,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	sachi@...tralsolutions.com,
	davinci-linux-open-source@...ux.davincidsp.com,
	Netdev@...r.kernel.org, nsekhar@...com,
	open list <linux-kernel@...r.kernel.org>,
	CAN NETWORK DRIVERS <socketcan-core@...ts.berlios.de>,
	m-watkins@...com
Subject: Re: [PATCH v4 1/1] can: add pruss CAN driver.

Hi Kurt,

On 05/04/2011 05:57 PM, Kurt Van Dijck wrote:
>>
>>> 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.
> ack.
>>
>>> 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.
> 
> When doing so, I'd vote for an unlimited(by software) list of hardware filters (id/mask).
> The hardware must abort when no more filters are available.

Sounds good and not even to complicated. For the SJA1000 we would just
allow to set the global mask.

> I think that when using hardware filters, knowing the actual device
> with it's amount of hardware filters is the least of your problems.
> Userspace applications that suddenly stop working properly due to
> hw filters (i.e. some traffic not coming in anymore) will be a major
> source of bugreports.

Well, hardware filtering will be off by default and must explicitly be
set by the user, like for the bitrate setting.

Wolfgang.

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