Re: [PATCH i-g-t v7 05/48] lib/igt_kms: Add helper to wait for new connectors

[Kory Maincent <kory.maincent@bootlin.com>]

On Mon, 23 Feb 2026 13:09:12 +0100
Louis Chauvet <louis.chauvet@bootlin.com> wrote:

> Add list comparison utilities and a new function to wait for new
> connectors to appear on the system.
> 
> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
> ---
>  lib/igt_kms.c | 96
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ lib/igt_kms.h |
> 6 ++++ 2 files changed, 102 insertions(+)
> 
> diff --git a/lib/igt_kms.c b/lib/igt_kms.c
> index 8876ee8a11f7..514d905fe1fe 100644
> --- a/lib/igt_kms.c
> +++ b/lib/igt_kms.c
> @@ -8170,3 +8170,99 @@ uint32_t igt_get_connector_id_from_mst_path(int
> drm_fd, const void *mst_path) 
>  	return 0;
>  }
> +
> +/**
> + * list_contains() - Search an element in the list
> + *
> + * @list: Pointer to the list to search into
> + * @list_len: Length of the list
> + * @value: Value to search in the list
> + *
> + * Returns true if @list contains @value
> + */
> +static bool list_contains(const uint32_t *list, int list_len, uint32_t value)
> +{
> +	igt_assert((!list && list_len == 0) || list);

You could simply do this here: igt_assert(list_len == 0 || list);


> +	for (int i = 0; i < list_len; i++) {
> +		if (list[i] == value)
> +			return true;
> +	}

You can remove the for loop bracket for a cleaner code.

> +	return false;
> +}
> +
> +/**
> + * get_list_diff() - Compute and return the set difference between two lists
> + *
> + * @list_a: Pointer to the first list to compare
> + * @list_a_len: Length of the first list
> + * @list_b: Pointer to the second list to compare
> + * @list_b_len: Length of the second list
> + * @diff: Out pointer returning a list of items in list_a but not
> + *        in list_b. Can be NULL to only count the elements.
> + *
> + * Returns the number of element which are in @list_a but not in @list_b.
> + */
> +int
> +get_list_diff(const uint32_t *list_a, int list_a_len, const uint32_t
> *list_b, int list_b_len,
> +	      uint32_t **diff)
> +{
> +	int diff_len = 0;
> +
> +	igt_assert((!list_a && list_a_len == 0) || list_a);
> +	igt_assert((!list_b && list_b_len == 0) || list_b);

Same here.

> +
> +	if (diff)
> +		*diff = malloc(sizeof(**diff));
> +
> +	for (int i = 0; i < list_a_len; i++) {
> +		if (!list_contains(list_b, list_b_len, list_a[i])) {
> +			if (diff) {
> +				*diff = reallocarray(*diff, diff_len + 1,
> sizeof(**diff));
> +				igt_assert(*diff);
> +				(*diff)[diff_len] = list_a[i];
> +			}
> +
> +			diff_len++;
> +		}
> +	}
> +
> +	return diff_len;
> +}
> +
> +/**
> + * kms_wait_for_new_connectors() - Wait for new connector to appear
> + *
> + * @newly_connected: Out pointer returning the list of connectors currently
> + *                   found connected
> + * @already_connected: Input pointer to list of connectors previously
> + *                     connected
> + * @already_connected_count: Length of @already_connected
> + * @drm_fd: DRM file descriptor
> + *
> + * Returns the number of connectors not in @already_connected and currently
> + * found connected.
> + */
> +int kms_wait_for_new_connectors(uint32_t **newly_connected,
> +				const uint32_t *already_connected,
> +				int already_connected_count, int drm_fd)
> +{
> +	int newly_connected_count;
> +	struct timespec start, end;
> +
> +	igt_assert(newly_connected);
> +	igt_assert(drm_fd);
> +
> +	clock_gettime(CLOCK_MONOTONIC, &start);
> +	clock_gettime(CLOCK_MONOTONIC, &end);
> +	do {
> +		if (*newly_connected)
> +			free(*newly_connected);
> +		newly_connected_count = igt_get_connected_connectors(drm_fd,
> newly_connected);
> +		clock_gettime(CLOCK_MONOTONIC, &end);
> +	} while (get_list_diff(*newly_connected, newly_connected_count,
> +			       already_connected, already_connected_count,
> +			       NULL) == 0 &&
> +		 igt_time_elapsed(&start, &end) <=
> igt_default_display_detect_timeout());

!get_list_diff(...)

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com