linux-kernel - Re: [PATCH 2/5] drivercore: Add driver probe deferral mechanism

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Date:	Fri, 7 Oct 2011 14:23:26 -0700
From:	Greg KH <greg@...ah.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	"G, Manjunath Kondaiah" <manjugk@...com>,
	linux-arm-kernel@...ts.infradead.org,
	Grant Likely <grant.likely@...retlab.ca>,
	linux-omap@...r.kernel.org, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org, Dilan Lee <dilee@...dia.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Manjunath@...per.es
Subject: Re: [PATCH 2/5] drivercore: Add driver probe deferral mechanism

On Fri, Oct 07, 2011 at 01:57:15PM -0700, Josh Triplett wrote:
> On Thu, Oct 06, 2011 at 11:49:28PM -0700, Greg KH wrote:
> > On Fri, Oct 07, 2011 at 10:33:07AM +0500, G, Manjunath Kondaiah wrote:
> > > +config PROBE_DEFER
> > > +	bool "Deferred Driver Probe"
> > > +	default y
> > > +	help
> > > +	  This option provides deferring driver probe if it has dependency on
> > > +	  other driver. Without this feature, initcall ordering should be done
> > > +	  manually to resolve driver dependencies. This feature completely side
> > > +	  steps the issues by allowing driver registration to occur in any
> > > +	  order, and any driver can request to be retried after a few more other
> > > +	  drivers get probed.
> > 
> > Why is this even an option?  Why would you ever want it disabled?  Why
> > does it need to be selected?
> > 
> > If you are going to default something to 'y' then just make it so it
> > can't be turned off any other way by just not making it an option at
> > all.
> 
> Given that the drivers which use this mechanism will not necessarily get
> built into the kernel, I'd suggest that it should remain optional and
> default to n.  Those drivers can then add a dependency on PROBE_DEFER.
> Let's try to avoid adding more infrastructure to the kernel that takes
> up space even when unused; certainly embedded will appreciate not having
> this feature unless a driver needs it.

How much extra space is this "feature" really?  I don't see it being
anything larger than the amount of memory increase that just happened as
I typed this email as part of the ongoing memory density changes.

greg k-h
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