Re: [PATCH 042/182] gpio: mpc8xxx: use gpiochip data pointer

[Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>]

Hello Linus,

On Wed, Dec 09, 2015 at 02:18:37PM +0100, Linus Walleij wrote:
> This makes the driver use the data pointer added to the gpio_chip
> to store a pointer to the state container instead of relying on
> container_of().

I wonder why your patch is an improvement. I imagine that container_of
is cheaper in instructions and memory/cache accesses. 

>  static void mpc8xxx_gpio_save_regs(struct of_mm_gpio_chip *mm)
>  {
> -	struct mpc8xxx_gpio_chip *mpc8xxx_gc = to_mpc8xxx_gpio_chip(mm);
> +	struct mpc8xxx_gpio_chip *mpc8xxx_gc = gpiochip_get_data(&mm->gc);
>  
>  	mpc8xxx_gc->data = in_be32(mm->regs + GPIO_DAT);
>  }

Also for my (subjective) eye the above change doesn't make the
assignment more readable.

So can you please expand your commit log (or rethink the patch)?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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