Re: [PATCH] drm/i915/scaler: Prune YUV420 modes against the max source width

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] drm/i915/scaler: missing vertical limit check for YUV420 modes
- [Medium] drm/i915/scaler: invalid joined pipe modes exposed due to skipped scaler limit check
--

commit 59a282a072c72ed078bc3b442b7aded1b908a674
Author: Arun R Murthy <arun.r.murthy@intel.com>

drm/i915/scaler: Prune YUV420 modes against the max source width

This commit updates the YUV420 mode validation in skl_scaler_mode_valid to
check the horizontal dimension against max_w instead of max_h. This fixes an
issue where single-pipe YUV420 modes were being evaluated against the vertical
scaler limits.

> diff --git a/drivers/gpu/drm/i915/display/skl_scaler.c b/drivers/gpu/drm/i915/display/skl_scaler.c
> index 7994b983d509d..7e65c4fffbc0c 100644
> --- a/drivers/gpu/drm/i915/display/skl_scaler.c
> +++ b/drivers/gpu/drm/i915/display/skl_scaler.c
> @@ -145,7 +145,7 @@ skl_scaler_mode_valid(struct intel_display *display,
>  
>  	if (num_joined_pipes < 2 && output_format == INTEL_OUTPUT_FORMAT_YCBCR420) {

[Severity: Medium]
By restricting this check to num_joined_pipes < 2, does this bypass the
scaler limit check for joined pipe modes?

When using Bigjoiner or Ultrajoiner (num_joined_pipes >= 2), the effective
per-pipe source width is mode->hdisplay / num_joined_pipes. If this effective
width still exceeds max_w, the mode will pass mode_valid but fail later
during the atomic_check phase in skl_update_scaler, potentially causing a
failed modeset or black screen.

>  		skl_scaler_max_src_size(display, &max_w, &max_h);
> -		if (mode->hdisplay > max_h)
> +		if (mode->hdisplay > max_w)

[Severity: Medium]
Does this code also need to validate the vertical dimension against max_h?

The function skl_scaler_max_src_size populates both max_w and max_h, but only
the horizontal dimension is checked. On Display 11, a maximum height up to
4320 is allowed by intel_mode_valid_max_plane_size, but the scaler's max_h
limit is 4096.

If a YUV420 mode with a vdisplay greater than 4096 is evaluated, it will pass
this check but could fail with -EINVAL during atomic commit in
skl_update_scaler when src_h exceeds the scaler limits.

>  			return MODE_NO_420;
>  	}
>

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261007070601.3611674-1-arun.r.murthy@intel.com?part=1