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

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Message-ID: <CACRpkdbXvf8mRgpr2MrmcJcT1gTg4mfBOnF8s3=+jS5iAcMtkQ@mail.gmail.com>
Date:	Tue, 5 Feb 2013 19:01:34 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Alexandre Courbot <acourbot@...dia.com>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	gnurou@...il.com
Subject: Re: [PATCH 8/9] gpiolib: use gpio_chips list in gpio_to_desc

On Sat, Feb 2, 2013 at 5:29 PM, Alexandre Courbot <acourbot@...dia.com> wrote:

> Parse the list of chips to find the descriptor corresponding to a GPIO
> number instead of directly picking the entry of the global gpio_desc[]
> array, which is due to be removed.
>
> This turns the complexity of converting a GPIO number into a descriptor
> from O(1) to O(n) where n is the number of GPIO chips in the system.
> Since n is ought to be small anyway, there should be no noticeable
> performance impact. Moreover, GPIO users who care for speed already have
> implemented their own gpio_get_value() and gpio_set_value() with a
> fast path for the GPIO numbers that matter and this change does not
> affect such use cases.
>
> The descriptor-based GPIO API, due to be introduced soon, will make this
> lookup unnecessary.
>
> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>

OK it's a nice stepping stone.

Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij
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