Changes between Version 4 and Version 5 of venice/ethernet

Timestamp:

01/04/2023 06:58:09 PM (2 years ago)

Author:

Ryan Erbstoesser

Comment:

add 74xx info

venice/ethernet

@@ -30 +30 @@
  * For boards like the GW740x which have a multi-port GbE switch, bandwidth is shared across the downstream ports
 
+== GW740x Ethernet Notes
+
+The GW740x has 6 RJ45's on the front panel. When looking at the board
+from the front with the user LED and barrel jack on the left these
+ports are:
+eth0 (IMX8MM EQOS MAC + GPY111 RGMII PHY)
+lan1 (KSZ9477 switch port from IMX8MM FEC MAC (eth1) CPU uplink)
+lan2 (KSZ9477 switch port from IMX8MM FEC MAC (eth1) CPU uplink)
+lan3 (KSZ9477 switch port from IMX8MM FEC MAC (eth1) CPU uplink)
+lan4 (KSZ9477 switch port from IMX8MM FEC MAC (eth1) CPU uplink)
+lan5 (KSZ9477 switch port from IMX8MM FEC MAC (eth1) CPU uplink)
+
+In U-Boot use the 'net list' command to show the available network
+devices as well as the 'eth' interface name and the device name that
+can be used to specify the active device in U-Boot. Either name can be
+set to the 'ethact' env variable to specify the active device and only
+1 device is active at a time for U-Boot network commands.
+
+Note that from the CPU's perspective 'eth1' is the CPU uplink device
+to the KSZ9477 switch so it is never used by itself.
+
+Example:
+# list network devs in U-Boot
+u-boot=> net list
+eth2 : lan1 00:d0:12:d3:f7:8e
+eth3 : lan2 00:d0:12:d3:f7:8f
+eth4 : lan3 00:d0:12:d3:f7:90
+eth5 : lan4 00:d0:12:d3:f7:91
+eth6 : lan5 00:d0:12:d3:f7:92
+eth1 : ethernet@30be0000 00:d0:12:d3:f7:8d
+eth0 : ethernet@30bf0000 00:d0:12:d3:f7:8c active
+# specify eth0 (the 1st RJ45) (this is also the default)
+setenv ethact eth0
+# specify lan1 (the 2nd RJ45)
+setenv ethact lan1 # or eth2 if you want but that is a U-Boot only name
+# save env if you want this to persist in U-Boot across boots
+saveenv
+
+For Linux, specifically our kernel and BSP you will see the device naming above:
+eth0 (IMX8MM EQOS MAC + GPY111 RGMII PHY)
+lan1 (KSZ9477 switch port from IMX8MM FEC MAC (eth1) CPU uplink)
+lan2 (KSZ9477 switch port from IMX8MM FEC MAC (eth1) CPU uplink)
+lan3 (KSZ9477 switch port from IMX8MM FEC MAC (eth1) CPU uplink)
+lan4 (KSZ9477 switch port from IMX8MM FEC MAC (eth1) CPU uplink)
+lan5 (KSZ9477 switch port from IMX8MM FEC MAC (eth1) CPU uplink)
+
+In Linux 5.12+ you do not need to bring up the CPU uplink port to the
+switch (eth1) as it will be brought up whenever any of the downstream
+ports are brought up. Modern Linux DSA (Distributed Switch
+Architecture) provides more or less full interface devices for the
+ports on the switch thus you can have IP configuration, VLAN etc, on
+the individual ports.
+
+Additionally our BSP is pre-configured to bring up eth0 with DHCP so
+if you have the first RJ45 plugged into your network you should see
+'eth0' properly configured for networking. If you want to use the 2nd
+RJ45 it would be 'lan1', etc.
+
+For Linux here are some gory details that you should be aware of if
+you stray from our kernel/BSP:
+In Linux things can be a bit more complicated depending on if you have
+systemd/udev changing device names or not. Linux will register
+on-board network devices as 'eth%d' starting at 0 and incrementing in
+the order the device is registered which depends greatly on the kernel
+(linking order, modules vs static drivers etc) and the kernel makes NO
+attempt to make this consistent across reboots. Therefore there is a
+concept in Linux where a userspace process like systemd/udev will
+rename the network interfaces as they get registered to use
+bus/port/path specific names that are consistent across boots. This
+produces pretty confusing names to most users so we disable this
+feature in our default build by passing 'net.ifnames=0' on the kernel
+command line which confusing enough is not at all a kernel option but
+systemd/udev parses the kernel cmdline to look for this. To make
+things worse DSA drivers (which modern switch devices are) get their
+port names from device-tree so Linux will name those 'lan1', 'lan2'.
+And to make things really worse because the IMX8MM FEC and EQOS
+network devices are different MAC's (both inside the IMX8MP) they have
+different drivers and those drivers can register in either order so
+eth0/eth1 can flip around across boots. I added a kernel patch (a
+controversial one that will never make it upstream) to our kernel to
+avoid this and make them consistent.
+
+Linux 5.12 DSA drivers will bring up the cpu port interface
+automatically which is why one may see eth1 up after bringing up any of
+the lan ports.
+
+
+