qemu: buildroot: always enable networking

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>

common.mk

@@ -37,9 +37,6 @@ CCACHE ?= $(shell which ccache) # Don't remove this comment (space is needed)
 QEMU_VIRTFS_ENABLE		?= n
 QEMU_VIRTFS_HOST_DIR	?= $(ROOT)
 
-# Enable SLiRP user networking
-QEMU_USERNET_ENABLE		?= n
-
 ################################################################################
 # Mandatory for autotools (for specifying --host)
 ################################################################################
@@ -309,10 +306,8 @@ QEMU_EXTRA_ARGS +=\
 	-device virtio-9p-device,fsdev=fsdev0,mount_tag=host
 endif
 
-ifeq ($(QEMU_USERNET_ENABLE),y)
-QEMU_EXTRA_ARGS +=\
-	-netdev user,id=vmnic -device virtio-net-device,netdev=vmnic
-endif
+# Enable QEMU SLiRP user networking
+QEMU_EXTRA_ARGS += -netdev user,id=vmnic -device virtio-net-device,netdev=vmnic
 
 define run-help
 	@echo
@@ -511,10 +506,8 @@ filelist-tee-common: optee-client xtest optee-examples
 		echo "file /lib/libyaml-0.so.2.0.5 $(LIBYAML_LIB_OUT)/libyaml-0.so.2.0.5 755 0 0" \
 									>> $(fl); \
 	fi
-	@if [ "$(QEMU_USERNET_ENABLE)" = "y" ]; then \
-		echo "slink /etc/rc.d/S02_udhcp_networking /etc/init.d/udhcpc 755 0 0" \
-		>> $(fl); \
-	fi
+	@echo "slink /etc/rc.d/S02_udhcp_networking /etc/init.d/udhcpc 755 0 0" \
+									>> $(fl);
 	@echo "# Secure storage dir" 					>> $(fl)
 	@echo "dir /data 755 0 0" 					>> $(fl)
 	@echo "dir /data/tee 755 0 0" 					>> $(fl)

docs/qemu.md

@@ -45,12 +45,14 @@ To mount host folder in QEMU, simply run:
 ```bash
 $ mount -t 9p -o trans=virtio host <mount_point>
 ```
-# 5. SLiRP user networking
-To enable SLiRP user networking just set `QEMU_USERNET_ENABLE ?= y` in `common.mk`.
-After booting QEMU VM, eth0 will automatically receive IP address via DHCP
+# 5. Networking
+After booting the QEMU VM, `eth0` will automatically receive an IP address from
+QEMU via DHCP thanks to the SLiRP user networking feature. QEMU will act as a
+gateway to the host network [SLiRP].
 
-*Important* Take into account that ICMP doesn't work in SLiRP mode,
-so `ping` utility won't work.
+Please note that ICMP won't work in the guest unless additional configuration is
+made, so the `ping` utility won't work.
 
 [bios]: https://github.com/linaro-swg/bios_qemu_tz_arm
 [README.md]: ../README.md
+[SLiRP]: https://wiki.qemu.org/Documentation/Networking#User_Networking_.28SLIRP.29