From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wolfgang Grandegger Subject: Re: [PATCH v4 1/1] can: add pruss CAN driver. Date: Wed, 04 May 2011 16:33:59 +0200 Message-ID: <4DC163D7.9010309@grandegger.com> References: <1303474267-6344-1-git-send-email-subhasish@mistralsolutions.com> <201104271525.28512.arnd@arndb.de> <15AD189F851849F69A011B6F4D1DDB6C@subhasishg> <201105041511.54095.arnd@arndb.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: sachi-EvXpCiN+lbve9wHmmfpqLFaTQe2KTcn/@public.gmane.org, davinci-linux-open-source-VycZQUHpC/PFrsHnngEfi1aTQe2KTcn/@public.gmane.org, Subhasish Ghosh , nsekhar-l0cyMroinI0@public.gmane.org, open list , CAN NETWORK DRIVERS , Marc Kleine-Budde , Netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, m-watkins-l0cyMroinI0@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org To: Arnd Bergmann Return-path: In-Reply-To: <201105041511.54095.arnd-r2nGTMty4D4@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: socketcan-core-bounces-0fE9KPoRgkgATYTw5x5z8w@public.gmane.org Errors-To: socketcan-core-bounces-0fE9KPoRgkgATYTw5x5z8w@public.gmane.org List-Id: netdev.vger.kernel.org Hi Arnd, On 05/04/2011 03:11 PM, Arnd Bergmann wrote: > On Wednesday 04 May 2011, Subhasish Ghosh wrote: >> CAN requires mail box IDs to be programmed in. But, the socket >> CAN subsystem supports only software filtering of the mail box IDs. >> >> So, the mail box IDs programmed into socket CAN during initialization >> does not propagate into the hardware. This is planned to be a future >> implementation in Socket CAN. >> >> In our case, we support hardware filtering, to work around with this, >> Wolfgang (Socket CAN owner) suggested that we implement >> this using sysfs. >> >> These setting are not for debugging, but to program the mail box IDs >> into the hardware. > > Ok, I see. Can you point me to that discussion? > > 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. 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. > 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. > 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. Wolfgang.