"Unnamed/non-netdev P2P-device" purpose ?
gdoffe opened this issue · 4 comments
Hello everyone,
The generic behavior I describe further was reproduced on Pi4 and CM3+ using various contexts: custom Yocto Dunfell Linux distribution or Raspberry Pi OS with linux-rpi kernel or mainline kernel.
Both Pi4 and CM3+ are using a BCM43455 WiFi/BLE combo chip.
My need is the following: having the AP + Managed modes working at the same time. But if the Managed interface change its frequency due to new connection, the AP frequency must follow dynamically Managed one.
To achieve this I use cypress/cyfmac43455-sdio.bin firmware from the mainline linux-firmware tag 20211216.
I create the wlan0_ap device using the following command:
/usr/sbin/iw dev wlan0 interface add wlan0_ap type __ap
It gives me the following interfaces:
root@revpi-cm3:~# iw dev
phy#0
Interface wlan0_ap
ifindex 5
wdev 0x2
addr c4:ac:59:79:85:d9
ssid TESTING_AP
type AP
channel 5 (2432 MHz), width: 20 MHz, center1: 2432 MHz
txpower 31.00 dBm
Interface wlan0
ifindex 4
wdev 0x1
addr c4:ac:59:79:85:d9
type managed
channel 5 (2432 MHz), width: 20 MHz, center1: 2432 MHz
txpower 31.00 dBm
In this configuration on my CM3, if I want to change the wlan0 connection for an other AP with an other channel, wlan0_ap channel does not follow the new wlan0 frequency.
I noticed on my Pi4 with a fresh install that there is a P2P-device interface that seems marked as Unnamed/non-netdev.
If I manually create this interface on my previous setup on CM3 (with this command), the magic happens and every time the managed interface connects to an other external AP, the wlan0_apinterface channels follow thewlan0` one.
/usr/sbin/iw dev wlan0 interface add wlan0_p2pdev type __p2pdev
root@revpi-cm3:~# iw dev
phy#0
Unnamed/non-netdev interface
wdev 0x3
addr c6:ac:59:79:85:d9
type P2P-device
Interface wlan0_ap
ifindex 5
wdev 0x2
addr c4:ac:59:79:85:d9
ssid TESTING_AP
type AP
channel 5 (2432 MHz), width: 20 MHz, center1: 2432 MHz
txpower 31.00 dBm
Interface wlan0
ifindex 4
wdev 0x1
addr c4:ac:59:79:85:d9
type managed
channel 5 (2432 MHz), width: 20 MHz, center1: 2432 MHz
txpower 31.00 dBm
So I have the expected behavior, but what is the purpose of this Unnamed/non-netdev P2P-device interface please ?
The "Issues" section is meant for problem reports, not random "I'm curious" questions. I can't give you an answer, other than the obvious "something to do with peer-to-peer networking". Presumably its useful to have a dedicated interface for it (separate IP addresses and controllability, etc.?), just as the AP and client interfaces are separate even though there is just one wireless chip.
@pelwell thank you so much for this very useful answer.
You got me right, I'm actually curious by nature. Just like the company I work for and who asks me why it is necessary to have a P2P-Device interface, when their 25 000 products based on a CM3+ just need a Managed and AP interfaces. 🤔
It becomes an issue/problem when you discover a such unusual behavior. For now, you closed the issue (thanks for that), without really answering it. We do not build products on doubts.
Non-answer let me think you do not know why this P2P-Device is needed. I'm fine with that, but just point me where I could find some help. If my understanding of this problem is not firmware related, point me on the possible source of the problem.
For now, the firmware from this repo is creating the Unnamed/non-netdev interface P2P-Device by default, the mainline linux-firmware does not. Why ?
This looks useful... Maybe you should start here:
For now, the firmware from this repo is creating the Unnamed/non-netdev interface P2P-Device by default, the mainline linux-firmware does not. Why ?
I think you are mistaken. Earlier you said:
I noticed on my Pi4 with a fresh install that there is a P2P-device [...]
This is where the difference lies, not in the wireless firmware.
Compare our firmware:
pi@raspberrypi:~$ dmesg | grep "Firmware: BCM4345"
[ 8.940717] brcmfmac: brcmf_c_preinit_dcmds: Firmware: BCM4345/6 wl0: Nov 1 2021 00:37:25 version 7.45.241 (1a2f2fa CY) FWID 01-703fd60
pi@raspberrypi:~$ iw dev
phy#0
Unnamed/non-netdev interface
wdev 0x2
addr de:a6:32:91:36:7c
type P2P-device
txpower 31.00 dBm
Interface wlan0
ifindex 3
wdev 0x1
addr dc:a6:32:91:36:7c
type managed
channel 116 (5580 MHz), width: 20 MHz, center1: 5580 MHz
txpower 31.00 dBm
with upstream firmware:
pi@raspberrypi:~$ dmesg | grep "Firmware: BCM4345"
[ 9.367518] brcmfmac: brcmf_c_preinit_dcmds: Firmware: BCM4345/6 wl0: Apr 15 2021 03:03:20 version 7.45.234 (4ca95bb CY) FWID 01-996384e2
pi@raspberrypi:~$ iw dev
phy#0
Unnamed/non-netdev interface
wdev 0x2
addr de:a6:32:91:36:7c
type P2P-device
txpower 31.00 dBm
Interface wlan0
ifindex 3
wdev 0x1
addr dc:a6:32:91:36:7c
type managed
channel 36 (5180 MHz), width: 20 MHz, center1: 5180 MHz
txpower 31.00 dBm
Raspberry Pi OS uses wpa_supplicant, and it is requesting the creation of the P2P device interface. Your Yocto build must be using a different configuration that doesn't request the P2P device, either because it doesn't use wpa_supplicant or because its wpa_supplicant is configured differently.