Re: [PATCH i-g-t 3/6] lib/igt_kms: Fix max_non_joiner_mode_found

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

On Wed, 01 Apr 2026, Kunal Joshi <kunal1.joshi@intel.com> wrote:
> Previously the function, instead of giving the highest possible mode the
> connector could support, started the check by looking if the mode was
> equal to max_pipe_hdisplay. There may be corner cases where a connector never supports the highest mode our source can
> drive (e.g. a 4K mode on a 5K-capable platform).
>
> Fix this by iterating all modes and tracking the best one (highest
> hdisplay, then highest clock as a tiebreaker) that does not require a
> big joiner, as determined by igt_bigjoiner_possible(). This correctly
> handles connectors with any max resolution.

I'm not requesting changes right now, but I keep wondering about having
the joiner code in igt_kms.[ch] at all. It's an Intel implementation
detail. Why is so much of that in the generic file instead of hidden in
some Intel specific file or directory?

BR,
Jani.


>
> v2: Reword commit message (Suraj)
>
> Fixes: 3830ca6a5068 ("lib/igt_kms: Add support to check joiner mode limit")
> Signed-off-by: Kunal Joshi <kunal1.joshi@intel.com>
> Reviewed-by: Mohammed Thasleem <mohammed.thasleem@intel.com>
> Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
> ---
>  lib/igt_kms.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/lib/igt_kms.c b/lib/igt_kms.c
> index 04b1f3972..dbd419a9b 100644
> --- a/lib/igt_kms.c
> +++ b/lib/igt_kms.c
> @@ -6979,21 +6979,26 @@ bool bigjoiner_mode_found(int drm_fd, drmModeConnector *connector,
>   * false otherwise.
>   */
>  bool max_non_joiner_mode_found(int drm_fd, drmModeConnector *connector,
> -			   int max_dotclock, drmModeModeInfo *mode)
> +			       int max_dotclock, drmModeModeInfo *mode)
>  {
> -	int max_hdisplay = get_max_pipe_hdisplay(drm_fd);
> +	bool found = false;
>  
>  	for (int i = 0; i < connector->count_modes; i++) {
>  		drmModeModeInfo *current_mode = &connector->modes[i];
>  
> -		if (current_mode->hdisplay == max_hdisplay &&
> -		    current_mode->clock < max_dotclock) {
> +		if (igt_bigjoiner_possible(drm_fd, current_mode, max_dotclock))
> +			continue;
> +
> +		if (!found ||
> +		    current_mode->hdisplay > mode->hdisplay ||
> +		    (current_mode->hdisplay == mode->hdisplay &&
> +		     current_mode->clock > mode->clock)) {
>  			*mode = *current_mode;
> -			return true;
> +			found = true;
>  		}
>  	}
>  
> -	return false;
> +	return found;
>  }
>  
>  /* TODO: Move these lib functions to the joiner-specific library file

-- 
Jani Nikula, Intel