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By this link we can see that in Pi 4 there is Wi-Fi module (called radio module under the picture).
But I can't figure out, how is this module connected to motherboard? Is this PCI bus or whatever?
Thanks in advance and sorry if it's obvious.

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    The WiFi module uses an internal bus that has no external controls or external interface. So it really doesn't matter what it uses since there's nothing you can change, access or influence.. – Dougie Oct 7 '20 at 14:20
  • @Dougie Thanks! So if there is some bug in wifi's firmware, the only way I can restart (or somehow refresh) its firmware is to do the full machine reboot? – budoattack Oct 7 '20 at 16:39
  • You can rmmod brcmfmac then modprobe it back in. That's effectively a reload of the firmware. – Dougie Oct 7 '20 at 19:22
  • @Dougie Unfortunately nope. It doesn't help. But full machine reboot helpes. Btw I'm struggling with some well-known bug in radio module firmware. And I want to avoid the full reboot. Do you know some way to do it? – budoattack Oct 8 '20 at 12:39
  • Mine work with RaspiOS 2020-08-20 - so perhaps you should try creating a new SDCard, booting that and running a test. – Dougie Oct 8 '20 at 17:00
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The radio module on a Pi4 is connected via SDIO:

$ ls /sys/bus/sdio/devices/mmc1\:0001\:1/net/
wlan0

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