NOUPSTREAM: drm: apple: Hide VRR behind a module parameter

Given that DCP requires a modeset to activate VRR, and given that
this is explicitly banned by KMS API contract and VESA DisplayPort
specification, hide this experimental support behind a module param.

Interestingly, the HDMI spec does not require a modeset-free VRR
transition. For this reason, it is expected that the KMS API contract
may change in the future, as both Intel and AMD hardware require
a modeset to enable VRR in some circumstances. Either VRR will be
expected to be enabled whenever it is supported, *or* modesetting
to toggle it on or off will be allowed. When that happens, this
commit *must* be reverted.

Signed-off-by: James Calligeros <jcalligeros99@gmail.com>

Author: chadmed

drivers/gpu/drm/apple/dcp.c

@@ -58,6 +58,10 @@ static bool unstable_edid = true;
 module_param(unstable_edid, bool, 0644);
 MODULE_PARM_DESC(unstable_edid, "Enable unstable EDID retrival support");
 
+bool vrr;
+module_param(vrr, bool, 0644);
+MODULE_PARM_DESC(vrr, "Enable Adaptive Sync/ProMotion on supported displays");
+
 /* copied and simplified from drm_vblank.c */
 static void send_vblank_event(struct drm_device *dev,
 		struct drm_pending_vblank_event *e,

drivers/gpu/drm/apple/iomfb_template.c

@@ -34,6 +34,8 @@
 /* Register defines used in bandwidth setup structure */
 #define REG_DOORBELL_BIT(idx) (2 + (idx))
 
+extern bool vrr;
+
 struct dcp_wait_cookie {
 	struct kref refcount;
 	struct completion done;
@@ -546,9 +548,9 @@ static u8 dcpep_cb_prop_chunk(struct apple_dcp *dcp,
 static bool dcpep_process_chunks(struct apple_dcp *dcp,
 				 struct dcp_set_dcpav_prop_end_req *req)
 {
-	struct apple_connector *connector = dcp->connector;
+	// struct apple_connector *connector = dcp->connector;
 	struct dcp_parse_ctx ctx;
-	int ret, i;
+	int ret; //, i;
 
 	if (!dcp->chunks.data) {
 		dev_warn(dcp->dev, "ignoring spurious end\n");
@@ -590,14 +592,14 @@ static bool dcpep_process_chunks(struct apple_dcp *dcp,
 		dcp_set_dimensions(dcp);
 	}
 
-	if (connector) {
-		for (i = 0; i < dcp->nr_modes; i++) {
-			if (dcp->modes[i].vrr) {
-				drm_connector_set_vrr_capable_property(&connector->base, true);
-				break;
-			}
-		}
-	}
+	// if (connector) {
+	// 	for (i = 0; i < dcp->nr_modes; i++) {
+	// 		if (dcp->modes[i].vrr) {
+	// 			drm_connector_set_vrr_capable_property(&connector->base, true);
+	// 			break;
+	// 		}
+	// 	}
+	// }
 
 	return true;
 }
@@ -1263,8 +1265,8 @@ int DCP_FW_NAME(iomfb_modeset)(struct apple_dcp *dcp,
 
 	dcp->during_modeset = true;
 
-	if (mode->vrr)
-		dcp_set_adaptive_sync(dcp, dcp->vrr_enabled ? mode->min_vrr : 0, cookie);
+	if (mode->vrr && vrr)
+		dcp_set_adaptive_sync(dcp, mode->min_vrr, cookie);
 	else
 		dcp_set_digital_out_mode(dcp, false, &dcp->mode,
 					 complete_set_digital_out_mode, cookie);
@@ -1422,7 +1424,7 @@ void DCP_FW_NAME(iomfb_flush)(struct apple_dcp *dcp, struct drm_crtc *crtc, stru
 		req->clear = 1;
 	}
 
-	if (has_surface && (dcp->use_timestamps || crtc_state->vrr_enabled)) {
+	if (has_surface && (dcp->use_timestamps || crtc_state->vrr_enabled || vrr)) {
 		/*
 		 * TODO: ascertain with certainty what these timestamps
 		 * are. These names are guesses based on what macOS populates