Re: [PATCHv7] gpio: Remove VLA from gpiolib

[Geert Uytterhoeven]

Hi Laura,

On Fri, May 18, 2018 at 12:32 AM, Laura Abbott <labbott@xxxxxxxxxx> wrote:
> The new challenge is to remove VLAs from the kernel
> (see https://lkml.org/lkml/2018/3/7/621) to eventually
> turn on -Wvla.
>
> Using a kmalloc array is the easy way to fix this but kmalloc is still
> more expensive than stack allocation. Introduce a fast path with a
> fixed size stack array to cover most chip with gpios below some fixed
> amount. The slow path dynamically allocates an array to cover those
> chips with a large number of gpios.
>
> Reviewed-by: Phil Reid <preid@xxxxxxxxxxxxxxxxx>
> Reviewed-and-tested-by: Lukas Wunner <lukas@xxxxxxxxx>
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
> ---
> v7: Tweaked the Kconfig text to clarify the wording. Also fixed a few
> other comments from Geert, including the earlier suggestion to reduce
> the zeroing since I was wrong about that.

Thanks for the update!

With the minor nit below resolved:
Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

> --- a/drivers/gpio/Kconfig
> +++ b/drivers/gpio/Kconfig
> @@ -22,6 +22,18 @@ menuconfig GPIOLIB
>
>  if GPIOLIB
>
> +config GPIOLIB_FASTPATH_LIMIT
> +       int "Maximum number of GPIOs for fast path"
> +       range 16 512

While you can indeed fit 2 * 16 bits in a long, a lower limit of 16 doesn't
make much sense, as you will use 2 longs (mask + bits) anyway.
So please increase it to 32.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds