linux-kernel - Re: [PATCH 5/8] staging: vme: add functions for bridge module refcounting

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Message-ID: <20110809184944.GA28746@flamenco.cs.columbia.edu>
Date:	Tue, 9 Aug 2011 14:49:44 -0400
From:	"Emilio G. Cota" <cota@...ap.org>
To:	Martyn Welch <martyn.welch@...com>
Cc:	gregkh@...e.de, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/8] staging: vme: add functions for bridge module
 refcounting

On Tue, Aug 09, 2011 at 15:26:09 +0100, Martyn Welch wrote:
> On 09/08/11 14:24, Manohar Vanga wrote:
> > If we really don't want explicit module refcounting by drivers, can we perhaps use
> > the return value of the probe to automatically do this? eg. in vme_bus_probe() like
> > below:
> > 
> >     int ret = 0;
> >     ...
> >     vme_bridge_get(bridge);
> >     if (driver->probe)
> >             ret = driver->probe(vdev);
> >     if (ret)
> >         vme_bridge_put(bridge);
> >     return ret;
> > 
> > Just a thought. Feel free to shoot it down if you think it's the incorrect
> > approach :P
> > 
> 
> After looking at the PCI and RapidIO subsystems, I think this is probably the
> correct approach. I guess the only quiestion then is at which point is
> vme_bridge_put() called assuming the probe is successful. I guess at module
> unload time, though I haven't checked in the PCI and RapidIO code.

This works as long as all devices are tied to the driver
loading; i.e. when the devices can only be removed when the
driver is removed.  A device might go away while the driver
still manages other devices of the same kin; this is why
particular drivers explicitly manage the get/put in
.probe/.release.

In vme we may one day have hotplug (VME64x supports it IIRC),
but we're not quite there yet. One can remove devices from
sysfs anytime though.

I still think the original patch is the sane way to go.

		Emilio
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