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SubjectRe: [patch 2.6.25-rc5 1/2] gpiolib: dynamic gpio number allocation
Date
On Thursday 13 March 2008, Andrew Morton wrote:
> > > > Actually, I tried IDRs for a while and they broke platforms
> > > > which needed to initialize and use GPIOs early: before kmalloc
> > > > would work. A real PITA that was -- and slow too.
> > >
> > > If IDRs were slow, that linear search will be glacial.
> >
> > The slowness of IDRs was needing to use them for the
> > routine lookups ... versus the current array index,
> > which costs a fraction of an instruction cycle and
> > doesn't need separate locks.
> >
> > Or were you implying they should be used for something
> > other than mapping GPIO numbers to controllers/state?
>
> For dynamic allocation. There should be no need for lookups outside
> register/unregister.

So -- a secondary data structure used only for allocation?
With the primary one as it is now?

If allocation were a hotspot something like that might be
worth considering ... though such duplication is usually
error prone. But it's not; such allocation is a rarity.


> Where did the CONFIG_NR_GPIOS discussion disappear to?

http://marc.info/?l=linux-kernel&m=120545979527097&w=2

I could maybe see a CONFIG_NR_EXTRA_GPIOS.


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