How does onboard Wi-Fi get presented to the OS? Desktop Motherboard

I'm looking at motherboards and I'm debating on spending more for one with built-in Wi-Fi. I was wondering how this is presented to the OS. I'd like to use PCI pass-through, so I'm wondering if it uses PCI somehow or some other technology like USB.

The specific motherboard I'm looking at is the MSI z370 gaming carbon AC

https://www.msi.com/Motherboard/Z370-GAMING-PRO-CARBON-AC/Specification

I can't even find that it says it has Wi-Fi or Bluetooth but I Googled and that's what the AC stands for and apparently it's Intel based... Not a very specific spec sheet in my opinion. Id love to know what exact Wi-Fi card is used.

Update: seems I missed the details tab.... I now see the type of card. But I still want to confirm that it's presented as a PCI device.

FreeSoftwareServers

Posted 2018-04-11T03:24:48.317

Reputation: 962

It clearly states in the datasheet that this board has WiFi and Bluetooth, even specifying the chipset as an Intel Wireless-AC 8265, according to https://www.msi.com/pdf/presale_v2/Z370-GAMING-PRO-CARBON-AC and Google confirms that chipset is available for USB or PCIe interface, which one is implemented honestly isn't relevant as both are more than sufficient to handle the potential bandwidth needs. These answers are pretty easy to Google, took me just a few seconds.

– acejavelin – 2018-04-11T03:40:53.567

3@acejavelin how it's presented to the OS is extremely relevant as I'm looking to do PCI pass-through via IOMMU/VT-d. It is in fact the only reason I asked the question. – FreeSoftwareServers – 2018-04-11T03:42:32.820

2Your question hinted more that you couldn't verify if the board had WiFi and Bluetooth, sorry if I misunderstood. I would find it very unusual for a mainboard, especially a gaming one, to use USB as it's WiFi interface... It would use the PCIe interface. – acejavelin – 2018-04-11T03:44:27.627

@acejavelin I've never had a motherboard with onboard Wi-Fi other than laptops. I figured though, but for the money and time i wanted to confirm. Thanks, your comment plus the answer leave me 100% sure its pci based. – FreeSoftwareServers – 2018-04-11T03:48:22.460

@FreeSoftwareServers I updated my answer slightly. The wireless card is definitely an M.2 style adapter, which is then slotted onto a PCIe x1 card. So I'm fairly certain it must use a PCIe interface. However, there is a USB cable that needs to be attached, although for what purpose, I'm not entirely certain. Could be for the Bluetooth? – Michael Frank – 2018-04-11T04:05:48.373

You could consider getting the MSI Z370 SLI Plus instead of the Z370 Gaming Pro Carbon AC. The SLI Plus is significantly cheaper. Though it does not have wireless. But that allows you to spend the difference in a WLAN PCIe card. – sbecker – 2018-04-11T07:12:09.427

Answers

The details page you linked has this information on it:

Intel® Dual Band Wireless-AC 8265 card

Supports Wi-Fi 802.11 a/b/g/n/ac, dual band (2.4GHz, 5GHz) up to 867 Mbps speed.

Supports Dual Mode Bluetooth® 2.1, 2.1+EDR, 3.0, 4.0, BLE, 4.2

Following that, you can find on Intel Ark that this wireless card could be either PCIe or USB.

Finally, looking at the box art:

There's a PCIe card!

However... and this is where the plot thickens... The product manual reveals the following information:

A USB Cable?!

But then further along it also mentions the following:

Intel® Dual Band Wireless-AC 8265 card
* The Wireless card is pre-install in the M2_3 (M.2 Key E) slot.

There's also this diagram:

All in all, it's quite unclear how exactly this wireless card actually connects to the motherboard, so basically... I dunno?

Michael Frank

Posted 2018-04-11T03:24:48.317

Reputation: 7 412

9OMG I was so focused on the motherboard.... I didn't even look at the PCI card. For some reason I thought it was literally integrated into the board. It's just a separate accessory. I already own a similar accessory. So in essence you saved me $100 investment in a motherboard accessory I don't need. – FreeSoftwareServers – 2018-04-11T03:50:06.260

2I've seen motherboards have a mini PCIe slot right on the board, with such a card installed (probably just an OEM thing), but never a purely integrated chip. Even an integrated chip would probably still be PCIe though. Some weird laptops might connect it through USB but not likely these days. – LawrenceC – 2018-04-11T03:55:03.023

Lol... Wow! I totally missed that as well, but that seems to be a pretty clear answer. – acejavelin – 2018-04-11T03:55:03.987

@michaelfrank I'm actually quite familiar, like I said for some reason I thought it was literally part of the motherboard. The USB provides extra power. I believe you can use it without the USB but the Bluetooth will not work. – FreeSoftwareServers – 2018-04-11T04:07:35.957

@FreeSoftwareServers Good to know, I commented up above that I thought the USB might be for BT. – Michael Frank – 2018-04-11T04:08:21.463

4@michaelfrank this got me thinking that the USB is more than power because when I use PCI pass-through with a similar device only the Wi-Fi shows up. To pass through the Bluetooth it shows up as an available USB device. To get PCI pass-through to work I have to pass through both separately. – FreeSoftwareServers – 2018-04-11T04:14:16.360

Considering the WiFi card itself is connecting to the host card via M.2 it's almost certain to be using PCIe, since that's pretty much just a straight through physical adaptation. – isaacparrot – 2018-04-11T07:50:59.007

@LawrenceC Just an aside, for completeness - I've owned a mini ITX motherboard that had a properly integrated wi-fi card. The aerial mounted right on the motherboard, next to the onboard Ethernet etc. – Dan – 2018-04-11T10:35:49.980

@LawrenceC having the wifi as a separate module of some sort (PCIe, mini PCI, m.2, etc) is common with enthusiast boards because of FCC regulations. The part that the wifi module is on needs to be tested/approved/etc, if the wifi is in a stand alone module that module needs vetted once (and can be bought pre-vetted from a 3rd party). If it's built into the mobo then each mobo needs separate FCC approval. It's the same reason that even in models with soldered ram/SSDs the wifi module is a separate card. – Dan is Fiddling by Firelight – 2018-04-11T19:57:38.947

As Micheal Frank mentioned in his answer, the motherboard in question comes with a Intel® Dual Band Wireless-AC 8265 card, and Intel's ARK website states: "System Interface Type: PCIe, USB".

This means that the card needs both PCIe and USB to work, not either-or. Typically in these kinds of combo Wifi + Bluetooth cards, whether made by Intel, Atheros (now Qualcomm) or Broadcom, whether in MiniPCIe or m.2 form factor, the PCIe lanes connect the WiFi part, and the USB lanes connect the Bluetooth part.

For example, the following is a screenshot taken from Device Manager on a Windows 10 laptop, where menu "View -> Device by connection" is selected:

Similarly, on a Linux computer, the WiFi card will show up in lspci, and the Bluetooth card will show up in lsusb.

The MiniPCIe and m.2 connection specifications both include PCIe lanes and USB lanes, and for a combo WiFi + Bluetooth card to work properly, both protocols are required. The PCIe adapter provided with the motherboard routes PCIe lanes on the m.2 connector to the PCIe slot, and the USB lanes to the USB connector, where it must be plugged in to the motherboard's internal USB headers using the provided cable. If the cable is not connected, WiFi may work, but Bluetooth will not work. (Certain models of laptops may have either only PCIe lanes or only USB lanes connected on their MiniPCIe / m.2 slots, and if a combo card is plugged in to those slots, only one function will work.)

Since the OP would like to use PCI passthrough to present the wireless card to a virtual machine, both the PCIe device and the USB device must be passed through if WiFi and Bluetooth are both desired in the virtual machine. (Even then it may not work properly, because PCI passthrough is black magic, and many devices don't like it. I have attempted to pass through a simple PCIe WiFi card before, and never got it to work; your mileage may vary.)

twisteroid ambassador

Posted 2018-04-11T03:24:48.317

Reputation: 514

Good technical answer. +1 – Michael Frank – 2018-04-11T08:15:39.423

4This makes me wonder why the heck it was designed this way....if it has a PCIe interface, why not present as a PCIe switch with 2 devices, one being the Wi-Fi card and one being the bluetooth interface? It seems silly to require both interfaces at the same time. – alex.forencich – 2018-04-11T15:08:30.890

6@alex.forencich Think about it... which one would you choose if you were to design a card? Wifi via USB is less efficient (more overhead, less electrical power). Bluetooth via PCIe isn't defined in the HCI specs, so you would have to integrate a PCIe USB host controller. – AndreKR – 2018-04-11T17:46:33.357

@twisteroidambassador I to have had trouble passing through a Wi-Fi PCI Nic. I have only been successful with esxi and even then not 100% of the time. I noticed in esxi 6.5 that the USB Bluetooth was no longer present but in esxi 6 it was. I completely was unable to do it via KVM passthrough. – FreeSoftwareServers – 2018-04-11T23:25:28.817

@AndreKR obviously wi-fi would have to be connected via PCIe to get the necessary bandwidth. Interesting to note that USB is the only 'standard' way to provide a bluetooth interface, that I was not aware of. Obviously there must be some advantage to adding the USB interface electronics and drivers instead of implementing a PCIe switch, USB host, and USB device, all on the same die. It's probably just the cheapest solution, after considering die area, testing, driver software, etc. – alex.forencich – 2018-04-12T01:21:29.247