netdev - Re: [PATCH 3/3] can: at91_can: make can

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Message-ID: <20110111134300.GA387@e-circ.dyndns.org>
Date:	Tue, 11 Jan 2011 14:43:00 +0100
From:	Kurt Van Dijck <kurt.van.dijck@....be>
To:	Wolfgang Grandegger <wg@...ndegger.com>
Cc:	Marc Kleine-Budde <mkl@...gutronix.de>,
	Socketcan-core@...ts.berlios.de, netdev@...r.kernel.org
Subject: Re: [PATCH 3/3] can: at91_can: make can_id of mailbox 0
 configurable

On Tue, Jan 11, 2011 at 02:28:36PM +0100, Wolfgang Grandegger wrote:
> 
> On 01/11/2011 01:33 PM, Marc Kleine-Budde wrote:
> > On 01/11/2011 01:27 PM, Wolfgang Grandegger wrote:
> >> On 01/11/2011 12:56 PM, Marc Kleine-Budde wrote:
> >>> On 01/11/2011 12:45 PM, Wolfgang Grandegger wrote:
> >>>> On 01/11/2011 11:28 AM, Marc Kleine-Budde wrote:
> >>>>> Due to a chip bug (errata 50.2.6.3 & 50.3.5.3 in
> >>>>> "AT91SAM9263 Preliminary 6249H-ATARM-27-Jul-09") the contents of mailbox
> >>>>> 0 may be send under certain conditions (even if disabled or in rx mode).
> >>>>>
> >>>>> The workaround in the errata suggests not to use the mailbox and load it
> >>>>> with a unused identifier.
> >>>>>
> >>>>> This patch implements the second part of the workaround. A sysfs entry
> >>>>> "mb0_id" is introduced. While the interface is down it can be used to
> >>>>> configure the can_id of mailbox 0. The default value id 0x7ff.
> >>>>>
> >>>>> In order to use an extended can_id add the CAN_EFF_FLAG (0x80000000U)
> >>>>> to the can_id. Example:
> >>>>>
> >>>>> - standard id 0x7ff:
> >>>>> echo 0x7ff      > /sys/class/net/can0/mb0_id
> >>>>>
> >>>>> - extended if 0x1fffffff:
> >>>               ^^
> >>> I've fixed the typo on my git repo. I'll send an updated series later.
> >>>
> >>>>> echo 0x9fffffff > /sys/class/net/can0/mb0_id
> >>>>
> >>>> As this is a device specific property, I think it should go into
> >>>> /sys/class/net/can0/device/.
> >>>
> >>> The attribute goes autoamtically to /sys/class/net/can0 if you add it to
> >>> the driver via:
> >>>
> >>> +       dev->sysfs_groups[0] = &at91_sysfs_attr_group;
> >>>
> >>> I've copied this from the janz-ican3 driver[1].
> >>
> >> Oh, I missed that. And also the Softing driver does it that way :-(. The
> >> member has the comment:
> >>
> >>   /* space for optional device, statistics, and wireless sysfs groups */
> >>   const struct attribute_group *sysfs_groups[4];
> >>
> >> Therefore it seems to be legal to use it for device specific properties.
> > 
> > I'm not really happy with these sysfs approach, but it's quick
> > implemented. Is device specific rtnetlink an option here?
> 
> That's toooooooo heavy, I think. I personally would just use
> device_create_file for that purpose. But let's keep using sysfs_groups[]
> if nobody else complains.

sysfs_groups[0] has the advantage that it's ready during the uevent
(ie. for use in udev). device_create_file() may get online after the uevent...

Kurt

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