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Date: Thu, 13 Mar 2008 17:54:44 -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: > > > Shouldn't ARCH_NR_GPIOS be CONFIG_NR_GPIOS? > > > > No more than NR_IRQS is settable via Kconfig. And for > > rather similar reasons. :) > > What are those reasons? Keeping a lid on the amount of space wasted by unused table entries is one factor; it's an implementation tradeoff. In normal usage the number of IRQs (or GPIOs) is defined by the board (or system) design, and there's no real point to allowing more. That said, NR_IRQS is kind of inflexible. It's not easy to provide board-specific overrides for cases like having a few FPGAs or other external IRQ (or GPIO!) controllers which chain IRQs and plug into those tables... Both could use a way to extend a platform-defined minimum to support a configurable number of external controllers. Lacking that, both have somewhat ad-hoc solutions to make sure board variants can be set up with the same kernel. It basically boils down to making sure there are some extra entries at end-of-table, and policies to allocate them. - Dave -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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