Message-ID: <20120825202556.GC413@vandijck-laurijssen.be>
Date:	Sat, 25 Aug 2012 22:25:56 +0200
From:	Kurt Van Dijck <kurt.van.dijck@....be>
To:	Fabio Baltieri <fabio.baltieri@...il.com>
Cc:	Marc Kleine-Budde <mkl@...gutronix.de>, linux-can@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Wolfgang Grandegger <wg@...ndegger.com>
Subject: Re: [PATCH can-next v6] can: add tx/rx LED trigger support

On Sat, Aug 25, 2012 at 12:01:42AM +0200, Fabio Baltieri wrote:
> Hello Kurt,
> 
> On Fri, Aug 24, 2012 at 02:42:48PM +0200, Kurt Van Dijck wrote:
> > On Fri, Aug 24, 2012 at 01:28:16PM +0200, Marc Kleine-Budde wrote:
> > > On 08/24/2012 07:10 AM, Kurt Van Dijck wrote:
> > > > Hello,
> > > > 
> > > > I find the CAN led triggers an interesting thing.
> > > > 
> > > > And then, this scenario fell crossed my mind:
> > > > Imagine I do:
> > > > [insert CAN device: can0]
> > > > $ ip link set can0 name helga
> > > > [insert another CAN device: again 'can0']
> > > > 
> > > > Registering 'can0-tx' led trigger will fail for the second CAN device,
> > > > since that led trigger name is already reserved for CAN device 'helga'.
> > > Good point.
> 
> Yep, thanks for pointing that out!
> 
> Interface renaming was something I considered when I first wrote the
> code and I had the mac80211-led driver in mind, as that driver uses the
> phy name and not the netdev one for its triggers.
> 
> The reason why I did not care that much in the end is that on SoC based
> systems trigger-led association is made at probe time, based on data
> either from platform_data or devicetree, so I imagined that once the
> kernel is ported to the board and default triggers are set correctly at
> boot time, the userspace is free to rename CAN interfaces and nobody
> should notice... :^)
> 
> The thing I did not consider are hot-plug interfaces mixed with
> renaming, such as in the case you pointed out - it's probably not really
> common but still possible.
> 
> > > > I'm not sure how to fix such.
> > > > If 'rx' & 'tx' may be combined, reusing the netdev name may be possible?
> > > > Just wild thinking ...
> > > 
> > > I think the device's name (not netdev) is unique in the system and
> > > cannot be changed.
> >
> > but may contain several netdev's ...
> 
> Ouch.
> 
> > 
> > > 
> > > On my device tree enabled mx28 I'm talking about the "80032000.can" in:
> > 
> > You idea triggered another thougt: since control is put in device drivers,
> > why putting the name in the generic can_dev struct?
> 
> Why not?  That makes the API easy.

The code is not next to the data?
Anyway, I said the above because I think the led names need a per-device approach,
but the data is in common parts. That's where things start being complicated.
I understand the common part now because you mainly addressed the SoC based drivers.

> 
> > A more flexible approach to assign names is the key to success here.
> > The correct 'works in all conditions' approach is not yet in my sight :-(
> 
> Agreed.
> 
> What about using a combination of device name + an optional port index
> specified in devm_can_led_init()? (something like to platform_device names)
> Of course that would require changing the API for libraries like
> register_sja1000dev(), to add a port index.
> 
> Fabio
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-- 
Kurt Van Dijck
GRAMMER EiA ELECTRONICS
http://www.eia.be
kurt.van.dijck@....be
+32-38708534
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