[PATCH] drm/i915/intel_crtc: Warn and clamp if num_scalers exceeds SKL_NUM_SCALERS

[Jani Nikula]

On Thu, 07 Aug 2025, Ankit Nautiyal <ankit.k.nautiyal at intel.com> wrote:
> Add a drm_WARN_ON() in intel_crtc_init() to catch cases where
> crtc->num_scalers exceeds the expected SKL_NUM_SCALERS limit.
>
> This condition should not occur, as the number of scalers per pipe does not
> exceed two for current platforms, making SKL_NUM_SCALERS (2) a safer upper
> limit. However, if a platform ever gains more scalers per pipe than
> SKL_NUM_SCALERS, it could lead to issues when crtc->num_scalers is used to
> iterate over scaler_state->scalers.
>
> To prevent this, warn and clamp the value to SKL_NUM_SCALERS.
>
> Suggested-by: Jani Nikula <jani.nikula at intel.com>
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>

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

> ---
>  drivers/gpu/drm/i915/display/intel_crtc.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_crtc.c b/drivers/gpu/drm/i915/display/intel_crtc.c
> index a187db6df2d3..e262e686dc2b 100644
> --- a/drivers/gpu/drm/i915/display/intel_crtc.c
> +++ b/drivers/gpu/drm/i915/display/intel_crtc.c
> @@ -317,6 +317,9 @@ int intel_crtc_init(struct intel_display *display, enum pipe pipe)
>  	crtc->pipe = pipe;
>  	crtc->num_scalers = DISPLAY_RUNTIME_INFO(display)->num_scalers[pipe];
>  
> +	if (drm_WARN_ON(display->drm, crtc->num_scalers > SKL_NUM_SCALERS))
> +		crtc->num_scalers = SKL_NUM_SCALERS;
> +
>  	if (DISPLAY_VER(display) >= 9)
>  		primary = skl_universal_plane_create(display, pipe, PLANE_1);
>  	else

-- 
Jani Nikula, Intel