linux-kernel - Re: [PATCH 8/9] gpiolib: use gpio_chips list in gpio_to

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Date:	Sat, 9 Feb 2013 23:21:56 +0900
From:	Alexandre Courbot <acourbot@...dia.com>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	linux-arch <linux-arch@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 8/9] gpiolib: use gpio_chips list in gpio_to_desc

On Sat, Feb 9, 2013 at 6:58 PM, Grant Likely <grant.likely@...retlab.ca> wrote:
> I'm actually going to NAK this one. This is a hot path. Having a O(1)
> lookup from gpio number to gpio desc is important. I know you want to be
> rid of the gpio_desc table entirely, but in this case I think it is
> warranted. However, you can change the gpio_desc table to be a table of
> pointers to gpio_descs instead of a table of gpio_descs. That would save
> a lot of memory since unused GPIOs wouldn't have gpio_descs associated
> with them. It is also the mechanism used by the IRQ subsystem.

That would work - what I don't like is that it still ends being a
fixed-size static array that is not necessarily tailored to the
platform's needs. But I understand you don't want to punish the users
of the integer-based API, even though the penalty should really be
neglectable here.

Well, maybe I can try to come again with this once everybody uses GPIO
descriptors instead of integers. ;)

Alex.
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