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

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Date:	Thu, 13 Mar 2008 16:53:58 -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:
> On Thu, 13 Mar 2008 15:18:58 -0800
> David Brownell <david-b@...bell.net> wrote:
> 
> > On Thursday 13 March 2008, Andrew Morton wrote:
> > 
> > > hm.  I suppose that if someone want a huge number of GPIOs then we can
> > > convert this to a bitmap or an IDR tree easily enough.
> > 
> > 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?

- Dave
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