linux-kernel - Re: [patch 2.6.25-rc5 1/2] gpiolib: dynamic gpio number allocation

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Message-Id: <200803132252.58101.david-b@pacbell.net>
Date:	Thu, 13 Mar 2008 21:52:57 -0800
From:	David Brownell <david-b@...bell.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, avorontsov@...mvista.com
Subject: Re: [patch 2.6.25-rc5 1/2] gpiolib:  dynamic gpio number allocation

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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