Re: [PATCH v2 6/7] gpiolib: avoid krealloc() in gpiod_get_array()

[Andy Shevchenko]

On Tue, Nov 03, 2026 at 07:40:34PM -0800, 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 struct gpio_descs *gpio_descs_alloc(unsigned int count, struct gpio_desc *first_desc)
> +{
> +	struct gpio_device *gdev = gpiod_to_gpio_device(first_desc);
> +	struct gpio_array *array_info;
> +	struct gpio_descs *descs;
> +	size_t descs_size, alloc_size;
> +	unsigned int bitmap_size;
> +
> +	/*
> +	 * If pin hardware number of array member 0 is also 0, select
> +	 * its chip as a candidate for fast bitmap processing path.
> +	 */
> +	if (gpiod_hwgpio(first_desc) != 0)
> +		return kzalloc_flex(*descs, desc, count);
> +
> +	descs_size = struct_size(descs, desc, count);
> +	bitmap_size = BITS_TO_LONGS(max(gdev->ngpio, count));
> +	alloc_size = descs_size + struct_size(array_info, invert_mask, 3 * bitmap_size);
> +
> +	descs = kzalloc(alloc_size, GFP_KERNEL);
> +	if (!descs)
> +		return NULL;
> +
> +	array_info = (void *)descs + descs_size;
> +	array_info->get_mask = array_info->invert_mask + bitmap_size;
> +	array_info->set_mask = array_info->get_mask + bitmap_size;
> +
> +	array_info->desc = descs->desc;
> +	array_info->size = count;
> +	array_info->gdev = gdev;

> +	bitmap_set(array_info->get_mask, 0, count);
> +	bitmap_set(array_info->set_mask, 0, count);

You don't need these, as memory is nullified.
Also note that we have bitmap_clear() IIRC.

> +	descs->info = array_info;
> +
> +	return descs;
> +}

...

>  		dev_dbg(dev,
>  			"GPIO array info: chip=%s, size=%d, get_mask=%lx, set_mask=%lx, invert_mask=%lx\n",
> -			array_info->gdev->label, array_info->size,
> -			*array_info->get_mask, *array_info->set_mask,
> -			*array_info->invert_mask);
> +			descs->info->gdev->label, descs->info->size,
> +			*descs->info->get_mask, *descs->info->set_mask,
> +			*descs->info->invert_mask);

Why not using %*pb for masks?

-- 
With Best Regards,
Andy Shevchenko