SoC/CPU and Ethernet controller internal connection in Raspberry Pi 3

Question

Raspberry Pi 3 uses SMSC LAN9514-JZX USB and Ethernet controller. While I read the LAN9514 manual, I quite did not understand how Ethernet controller interacts with SoC/CPU. Block diagram from manual can be seen below:

Manual states that USB hub has Four downstream ports, one upstream port. Does this mean that all the USB peripheral devices AND Ethernet controller share the single USB port to SoC/CPU also in Raspberry Pi 3? If yes, then does this mean that this Ethernet controller appears as am USB Ethernet controller in OS?

Answer 1

Does this mean that all the USB peripheral devices AND Ethernet controller share the single USB port to SoC/CPU also in Raspberry Pi 3?

Yes. All USB ports and the ethernet jack have a combined maximum throughput equal to one USB 2.0 port. It is not uncommon for computers of all sorts to combine several USB ports on one hub this way, although including an ethernet adapter is (I believe the LAN9415 may actually be the first thing of this kind). So if you are reading 5 MB/s through the ethernet then writing it back out to a USB device, that (minimally) amounts to 10 MB/s throughput on the bus.

If yes, then does this mean that this Ethernet controller appears as am USB Ethernet controller in OS?

Yes. Here's something you'll see in the output from lsusb:

 Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp. SMSC9512/9514 Fast Ethernet Adapter

And there is a driver for this device in the vanilla linux kernel under drivers/net/usb, smsc95xx. I presume this is built into the pre-compiled pi kernel (i.e., it is not built as a separate module) since you will not see it listed under lsmod nor find it in the /lib/modules/n.n.n directory. However, as noted here, you need to include it when you are building a custom kernel (it might be that it has to be built in, i.e., cannot be a separate .ko., I don't remember).