drm/hyperv: Handle feature change message from device

Virtual device inform if screen update is needed or not with
SYNTHVID_FEATURE_CHANGE message. Handle this message to set dirt_needed
flag.

Suggested-by: Dexuan Cui <[e-mail]>
Signed-off-by: Deepak Rawat <[e-mail]>
Acked-by: Thomas Zimmermann <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/hyperv/hyperv_drm.h

···
 	struct completion wait;
 	u32 synthvid_version;
 	u32 mmio_megabytes;
+	bool dirt_needed;
 
 	u8 init_buf[VMBUS_MAX_PACKET_SIZE];
 	u8 recv_buf[VMBUS_MAX_PACKET_SIZE];

drivers/gpu/drm/hyperv/hyperv_drm_drv.c

···
 	if (ret)
 		drm_warn(dev, "Failed to update vram location.\n");
 
+	hv->dirt_needed = true;
+
 	ret = hyperv_mode_config_init(hv);
 	if (ret)
 		goto err_vmbus_close;

drivers/gpu/drm/hyperv/hyperv_drm_proto.c

···
 
 int hyperv_update_dirt(struct hv_device *hdev, struct drm_rect *rect)
 {
+	struct hyperv_drm_device *hv = hv_get_drvdata(hdev);
 	struct synthvid_msg msg;
+
+	if (!hv->dirt_needed)
+		return 0;
 
 	memset(&msg, 0, sizeof(struct synthvid_msg));
 
···
 		complete(&hv->wait);
 		return;
 	}
+
+	if (msg->vid_hdr.type == SYNTHVID_FEATURE_CHANGE)
+		hv->dirt_needed = msg->feature_chg.is_dirt_needed;
 }
 
 static void hyperv_receive(void *ctx)