Re: [PATCH i-g-t v2 04/11] lib/kms: Get rid of the 'p' plane index variable

[Jani Nikula <jani.nikula@intel.com>]

On Thu, 18 Dec 2025, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> The 'p' thing used to track the next free plane slot is annoying.
> Get rid of it by just initializing the plane indexes to -1 to
> indicate a free slot at the start, and then do a straightforward
> search for the next free slot. And for good measure make sure all
> the -1's have disappeared at the end.
>
> v2: Remove spurious whitespace (Jani)
>     Fix the post init plane->index assert (Jani/CI)
>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

> ---
>  lib/igt_kms.c | 42 +++++++++++++++++++++++++-----------------
>  1 file changed, 25 insertions(+), 17 deletions(-)
>
> diff --git a/lib/igt_kms.c b/lib/igt_kms.c
> index 72c91fb5da76..803a1e926b10 100644
> --- a/lib/igt_kms.c
> +++ b/lib/igt_kms.c
> @@ -3057,7 +3057,7 @@ static void igt_crtc_init(igt_display_t *display,
>  {
>  	igt_crtc_t *pipe = igt_crtc_for_pipe(display, i);
>  	igt_plane_t *plane;
> -	int p = 1, crtc_mask = 0;
> +	int crtc_mask = 0;
>  	int j, type;
>  
>  	pipe->display = display;
> @@ -3085,10 +3085,14 @@ static void igt_crtc_init(igt_display_t *display,
>  	igt_assert_f(pipe->planes, "Failed to allocate memory for %d planes\n",
>  		     pipe->n_planes);
>  
> +	for (j = 0; j < pipe->n_planes; j++)
> +		pipe->planes[j].index = -1;
> +
>  	/* add the planes that can be used with that pipe */
>  	for (j = 0; j < display->n_planes; j++) {
>  		igt_plane_t *global_plane = &display->planes[j];
>  		drmModePlane *drm_plane = global_plane->drm_plane;
> +		int index;
>  
>  		if (!(drm_plane->possible_crtcs & crtc_mask))
>  			continue;
> @@ -3096,29 +3100,36 @@ static void igt_crtc_init(igt_display_t *display,
>  		type = global_plane->type;
>  
>  		if (type == DRM_PLANE_TYPE_PRIMARY && pipe->plane_primary == -1) {
> -			plane = &pipe->planes[0];
> -			plane->index = 0;
> -			pipe->plane_primary = 0;
> +			index = 0;
> +
> +			pipe->plane_primary = index;
>  			pipe->num_primary_planes++;
>  		} else if (type == DRM_PLANE_TYPE_CURSOR && pipe->plane_cursor == -1) {
> -			plane = &pipe->planes[pipe->n_planes - 1];
> -			plane->index = pipe->n_planes - 1;
> -			pipe->plane_cursor = pipe->n_planes - 1;
> +			index = pipe->n_planes - 1;
> +
> +			pipe->plane_cursor = index;
>  			display->has_cursor_plane = true;
>  		} else {
> +			for (index = 1; index < pipe->n_planes; index++) {
> +				if (pipe->planes[index].index < 0)
> +					break;
> +			}
> +
>  			/*
>  			 * Increment num_primary_planes for any extra
>  			 * primary plane found.
>  			 */
>  			if (type == DRM_PLANE_TYPE_PRIMARY)
>  				pipe->num_primary_planes++;
> -
> -			plane = &pipe->planes[p];
> -			plane->index = p++;
>  		}
>  
> -		igt_assert_f(plane->index < pipe->n_planes,
> -			     "n_planes < plane->index failed\n");
> +		igt_assert_lt(index, pipe->n_planes);
> +
> +		plane = &pipe->planes[index];
> +
> +		igt_assert_lt(plane->index, 0);
> +
> +		plane->index = index;
>  		plane->type = type;
>  		plane->pipe = pipe;
>  		plane->drm_plane = drm_plane;
> @@ -3143,11 +3154,8 @@ static void igt_crtc_init(igt_display_t *display,
>  	 */
>  	igt_assert_eq(pipe->plane_primary, 0);
>  
> -	/* Check that we filled every slot exactly once */
> -	if (display->has_cursor_plane)
> -		igt_assert_eq(p, pipe->n_planes - 1);
> -	else
> -		igt_assert_eq(p, pipe->n_planes);
> +	for (j = 0; j < pipe->n_planes; j++)
> +		igt_assert_lte(0, pipe->planes[j].index);
>  }
>  
>  /**

-- 
Jani Nikula, Intel