drm/vc4: vec: Check for VEC output constraints

The VEC can accept pretty much any relatively reasonable mode, but still
has a bunch of constraints to meet.

Let's create an atomic_check() implementation that will make sure we
don't end up accepting a non-functional mode.
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Mateusz Kwiatkowski <kfyatek+publicgit@gmail.com>
Tested-by: Mateusz Kwiatkowski <kfyatek+publicgit@gmail.com>
Acked-in-principle-or-something-like-that-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://lore.kernel.org/r/20220728-rpi-analog-tv-properties-v10-16-256dad125326@cerno.techSigned-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/vc4/vc4_vec.c

@@ -453,6 +453,7 @@ static int vc4_vec_encoder_atomic_check(struct drm_encoder *encoder,
 					struct drm_crtc_state *crtc_state,
 					struct drm_connector_state *conn_state)
 {
+	const struct drm_display_mode *mode = &crtc_state->adjusted_mode;
 	const struct vc4_vec_tv_mode *vec_mode;
 
 	vec_mode = &vc4_vec_tv_modes[conn_state->tv.legacy_mode];
@@ -461,6 +462,55 @@ static int vc4_vec_encoder_atomic_check(struct drm_encoder *encoder,
 	    !drm_mode_equal(vec_mode->mode, &crtc_state->adjusted_mode))
 		return -EINVAL;
 
+	if (mode->crtc_hdisplay % 4)
+		return -EINVAL;
+
+	if (!(mode->crtc_hsync_end - mode->crtc_hsync_start))
+		return -EINVAL;
+
+	switch (mode->htotal) {
+	/* NTSC */
+	case 858:
+		if (mode->crtc_vtotal > 262)
+			return -EINVAL;
+
+		if (mode->crtc_vdisplay < 1 || mode->crtc_vdisplay > 253)
+			return -EINVAL;
+
+		if (!(mode->crtc_vsync_start - mode->crtc_vdisplay))
+			return -EINVAL;
+
+		if ((mode->crtc_vsync_end - mode->crtc_vsync_start) != 3)
+			return -EINVAL;
+
+		if ((mode->crtc_vtotal - mode->crtc_vsync_end) < 4)
+			return -EINVAL;
+
+		break;
+
+	/* PAL/SECAM */
+	case 864:
+		if (mode->crtc_vtotal > 312)
+			return -EINVAL;
+
+		if (mode->crtc_vdisplay < 1 || mode->crtc_vdisplay > 305)
+			return -EINVAL;
+
+		if (!(mode->crtc_vsync_start - mode->crtc_vdisplay))
+			return -EINVAL;
+
+		if ((mode->crtc_vsync_end - mode->crtc_vsync_start) != 3)
+			return -EINVAL;
+
+		if ((mode->crtc_vtotal - mode->crtc_vsync_end) < 2)
+			return -EINVAL;
+
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
 	return 0;
 }