Why do need both "ipw2x00" and "brcm80211" for official Raspberry-PI WIFI dongle?

[snip]

Now got another question:

• I am using official Raspberry-PI WIFI dongle (BCM43143)
• So I re-start from "master" branch of meta-iot2000 (with original drivers: "ath, realtek")
• I configure kernel so that driver "brcm80211" is enabled, however, WIFI is not working
• Then I add driver "ipw2x00", then WIFI works.
• So my question, why do we need both "ipw2x00" and "brcm80211" for official Raspberry-PI WIFI dongle?
• (when I download sample image from this website, I saw drivers: "brcm80211, iwlwifi, rt2x00")
• (so I am confused, "ipw2x00 vs rt2x00(also iwlwifi?)", which is critical for my WIFI dongle?)

Thanks!

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Split from Latest SD-Card image compared to building from scratch.