drm/vc4: hdmi: Make sure our clock rate is within limits

The HDMI controller cannot go above a certain pixel rate limit depending on
the generations, but that limit is only enforced in mode_valid at the
moment, which means that we won't advertise modes that exceed that limit,
but the userspace is still free to try to setup a mode that would.

Implement atomic_check to make sure we check it in that scenario too.
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201029122522.1917579-1-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_hdmi.c

@@ -760,6 +760,20 @@ static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
 {
 }
 
+static int vc4_hdmi_encoder_atomic_check(struct drm_encoder *encoder,
+					 struct drm_crtc_state *crtc_state,
+					 struct drm_connector_state *conn_state)
+{
+	struct drm_display_mode *mode = &crtc_state->adjusted_mode;
+	struct vc4_hdmi *vc4_hdmi = encoder_to_vc4_hdmi(encoder);
+	unsigned long long pixel_rate = mode->clock * 1000;
+
+	if (pixel_rate > vc4_hdmi->variant->max_pixel_clock)
+		return -EINVAL;
+
+	return 0;
+}
+
 static enum drm_mode_status
 vc4_hdmi_encoder_mode_valid(struct drm_encoder *encoder,
 			    const struct drm_display_mode *mode)
@@ -773,6 +787,7 @@ vc4_hdmi_encoder_mode_valid(struct drm_encoder *encoder,
 }
 
 static const struct drm_encoder_helper_funcs vc4_hdmi_encoder_helper_funcs = {
+	.atomic_check = vc4_hdmi_encoder_atomic_check,
 	.mode_valid = vc4_hdmi_encoder_mode_valid,
 	.disable = vc4_hdmi_encoder_disable,
 	.enable = vc4_hdmi_encoder_enable,