drm/i915: Introduce intel_mode_vdisplay()

The DSB code will need to know the hardware's idea of vertical
active, as that is also what defines the start of undelayed
vblank. Introduce a helper that gives us that information,
in line with the other intel_mode_v*() functions.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240611133344.30673-5-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/display/intel_vblank.c

@@ -557,6 +557,16 @@ void intel_crtc_update_active_timings(const struct intel_crtc_state *crtc_state,
 	spin_unlock_irqrestore(&i915->drm.vblank_time_lock, irqflags);
 }
 
+int intel_mode_vdisplay(const struct drm_display_mode *mode)
+{
+	int vdisplay = mode->crtc_vdisplay;
+
+	if (mode->flags & DRM_MODE_FLAG_INTERLACE)
+		vdisplay = DIV_ROUND_UP(vdisplay, 2);
+
+	return vdisplay;
+}
+
 int intel_mode_vblank_start(const struct drm_display_mode *mode)
 {
 	int vblank_start = mode->crtc_vblank_start;

drivers/gpu/drm/i915/display/intel_vblank.h

@@ -20,6 +20,7 @@ struct intel_vblank_evade_ctx {
 	bool need_vlv_dsi_wa;
 };
 
+int intel_mode_vdisplay(const struct drm_display_mode *mode);
 int intel_mode_vblank_start(const struct drm_display_mode *mode);
 int intel_mode_vblank_end(const struct drm_display_mode *mode);
 int intel_mode_vtotal(const struct drm_display_mode *mode);