Re: [PATCH 1/4] gpio: Remove VLA from gpiolib

[Andy Shevchenko]

On Mon, Mar 19, 2018 at 9:00 AM, Lukas Wunner <lukas@xxxxxxxxx> wrote:
> On Sun, Mar 18, 2018 at 09:34:12PM +0100, Rasmus Villemoes wrote:
>> On 2018-03-18 15:23, Lukas Wunner wrote:

>> > Actually, scratch that.  If ngpio is usually smallish, we can just
>> > allocate reasonably sized space for mask and bits on the stack,
>> > and fall back to the kcalloc slowpath only if chip->ngpio exceeds
>> > that limit.

>> Well, I'd suggest not adding that fallback code now, but simply add a
>> check in gpiochip_add_data_with_key to ensure ngpio is sane (and refuse
>> to register the chip otherwise), at least if we know that every
>> currently supported/known chip is covered by the 256 (?).
>
> The number 256 was arbitrarily chosen.  I really wouldn't be surprised
> if gpiochips with more pins exist, but they're probably rare, so using
> the slowpath seems fine, but dropping support for them completely would
> be a regression.

All modern Intel SoCs have GPIO count in between of ~230-380.
Though, few of them are split to communities by (much) less than 256
pin in each when there is a 1:1 mapping between community and
gpiochip.

OTOH, the function you are fixing is most likely is not used together
with the drivers for x86.

-- 
With Best Regards,
Andy Shevchenko