Re: [PATCH 5/5] gpiolib: avoid krealloc() in gpiod_get_array()

[Andy Shevchenko]

On Wed, Oct 21, 2026 at 12:02:10PM -0700, Dmitry Torokhov wrote:
> Instead of allocating descs before the loop and reallocating it via
> krealloc() when candidate hardware array matching is detected on the
> first iteration, defer allocation of descs until the first descriptor
> is retrieved.
> 
> Factor descriptor allocation and fast-path validation into helper
> functions gpio_descs_alloc() and gpio_descs_check_fastpath(). Inside
> the loop, acquire the descriptor using __free(gpiod_put), allocate
> descs once on the first iteration, check fast-path candidate
> suitability, and transfer descriptor ownership using no_free_ptr().

...

> +static void gpio_descs_check_fastpath(struct gpio_descs *descs,
> +				      struct gpio_desc *desc)
> +{
> +	struct gpio_array *array_info = descs->info;

Split the assignment. It's robust for long-term maintenance to have assignment
coupled with a validation check.

> +	unsigned int idx = descs->ndescs;
> +	unsigned long dflags;


	array_info = desc->info;

> +	if (!array_info)
> +		return;
> +
> +	/* Unmark array members which don't belong to the 'fast' chip */
> +	if (array_info->gdev != gpiod_to_gpio_device(desc)) {
> +		__clear_bit(idx, array_info->get_mask);
> +		__clear_bit(idx, array_info->set_mask);
> +		return;
> +	}
> +
> +	/*
> +	 * Detect array members which belong to the 'fast' chip
> +	 * but their pins are not in hardware order.
> +	 */
> +	if (gpiod_hwgpio(desc) != idx) {
> +		/*
> +		 * Don't use fast path if all array members processed so
> +		 * far belong to the same chip as this one but its pin
> +		 * hardware number is different from its array index.
> +		 */
> +		if (bitmap_full(array_info->get_mask, idx)) {
> +			descs->info = NULL;
> +		} else {
> +			__clear_bit(idx, array_info->get_mask);
> +			__clear_bit(idx, array_info->set_mask);
> +		}
> +		return;
> +	}
> +
> +	dflags = READ_ONCE(desc->flags);
> +	/* Exclude open drain or open source from fast output */
> +	if (test_bit(GPIOD_FLAG_OPEN_DRAIN, &dflags) ||
> +	    test_bit(GPIOD_FLAG_OPEN_SOURCE, &dflags))
> +		__clear_bit(idx, array_info->set_mask);
> +
> +	/* Identify 'fast' pins which require invertion */
> +	if (gpiod_is_active_low(desc))
> +		__set_bit(idx, array_info->invert_mask);
> +}

-- 
With Best Regards,
Andy Shevchenko