[PATCH rtems-docs] zynqmp: Add commentary about lwIP usage

[Kinsey Moore]

---
 user/bsps/aarch64/xilinx-zynqmp.rst | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/user/bsps/aarch64/xilinx-zynqmp.rst b/user/bsps/aarch64/xilinx-zynqmp.rst
index 78bff12..58954d6 100644
--- a/user/bsps/aarch64/xilinx-zynqmp.rst
+++ b/user/bsps/aarch64/xilinx-zynqmp.rst
@@ -244,6 +244,15 @@ Cadence GEM instances present on all ZynqMP hardware variants. All interfaces
 are enabled by default, but only interfaces with operational MII busses will be
 recognized and usable in RTEMS. Most ZynqMP dev boards use CGEM3.
 
+When used with lwIP from the rtems-lwip integration repository, these BSP
+variants support networking via the 0th and any one other of the Cadence GEM
+instances simultaneously. This is a limitation of the Xilinx driver,
+specifically in code referring directly to XPAR_XEMACPS_0_BASEADDR.
+
+The interfaces will not come up by default under lwIP and must be configured
+manually. There are examples of this in the start_networking() implementation
+in netstart.c as used by the network tests.
+
 Running Executables on QEMU
 ---------------------------
 
-- 
2.30.2