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

Josh Triplett
2011-10-08T04:04:05Z

On Fri, Oct 07, 2011 at 02:23:26PM -0700, Greg KH wrote:
> 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?

Just checked: 776 bytes, 640 of text and 136 of data. We have kconfig
options for comparable amounts.

> 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.

I don't know about the changes you mean, but in any case I'd like to
prevent mandatory size increases wherever possible. I'd love to see the
size of "allnoconfig" getting *smaller* over time, not larger.

- Josh Triplett