drm/vc4: hdmi: Take our lock to reset the link

We access some fields protected by our internal mutex in
vc4_hdmi_reset_link() (saved_adjusted_mode, output_bpc, output_format)
and are calling functions that need to have that lock taken
(vc4_hdmi_supports_scrambling()).

However, the current code doesn't lock that mutex. Let's make sure it
does.

Fixes: 6bed2ea3 ("drm/vc4: hdmi: Reset link on hotplug")
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://lore.kernel.org/r/20221024093634.118190-1-maxime@cerno.techSigned-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/vc4/vc4_hdmi.c

@@ -349,27 +349,40 @@ static int vc4_hdmi_reset_link(struct drm_connector *connector,
 	if (!crtc_state->active)
 		return 0;
 
-	if (!vc4_hdmi_supports_scrambling(encoder))
+	mutex_lock(&vc4_hdmi->mutex);
+
+	if (!vc4_hdmi_supports_scrambling(encoder)) {
+		mutex_unlock(&vc4_hdmi->mutex);
 		return 0;
+	}
 
 	scrambling_needed = vc4_hdmi_mode_needs_scrambling(&vc4_hdmi->saved_adjusted_mode,
 							   vc4_hdmi->output_bpc,
 							   vc4_hdmi->output_format);
-	if (!scrambling_needed)
+	if (!scrambling_needed) {
+		mutex_unlock(&vc4_hdmi->mutex);
 		return 0;
+	}
 
 	if (conn_state->commit &&
-	    !try_wait_for_completion(&conn_state->commit->hw_done))
+	    !try_wait_for_completion(&conn_state->commit->hw_done)) {
+		mutex_unlock(&vc4_hdmi->mutex);
 		return 0;
+	}
 
 	ret = drm_scdc_readb(connector->ddc, SCDC_TMDS_CONFIG, &config);
 	if (ret < 0) {
 		drm_err(drm, "Failed to read TMDS config: %d\n", ret);
+		mutex_unlock(&vc4_hdmi->mutex);
 		return 0;
 	}
 
-	if (!!(config & SCDC_SCRAMBLING_ENABLE) == scrambling_needed)
+	if (!!(config & SCDC_SCRAMBLING_ENABLE) == scrambling_needed) {
+		mutex_unlock(&vc4_hdmi->mutex);
 		return 0;
+	}
+
+	mutex_unlock(&vc4_hdmi->mutex);
 
 	/*
 	 * HDMI 2.0 says that one should not send scrambled data