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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:
> On Thu, 13 Mar 2008 15:18:58 -0800
> David Brownell <david-b@pacbell.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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