So now it's in a box and on its way to BIL, who can now use it to test distros. Win/win. To all who responded, thanks for all your help!
First, my sincere apologies if this is a stupid noob question. I have a lot of tech experience but virtually none with Linux, so keep that in mind: I really have zero idea what to expect as I go along.
So I've been trying out multiple distros on my old mid-2010 MacBook, and have not had any problems at all: they have all seen my Broadcom wifi chip out of the box and just worked without a hitch.
On the other hand, my BIL (who heard about what I was up to and is now also trying out various distros via LiveUSB sticks I send him) has a MacBook Pro one year older, and NONE of the distros he's tried even see the onboard wifi. No wifi icon, no wifi in settings, it's like wifi doesn't exist. Ethernet shows up just fine, though.
When I looked into it further and had him do a specific lspci query to find out exactly what chipset he has, turns out he has a known problem: his particular MacBook Pro uses a Broadcom BMC4322 (432b) chip, which has only limited support under Linux via "wl" and maybe a "brcmsmac" driver written for legacy Broadcom wifi chips.
That's fine once he installs Linux, if he does, but right now he's just doing LiveUSB trials. We don't want to change anything on his existing hardware or HDD.
Okay, so maybe I can add some driver files to the LiveUSB or something? . . . nope. Not a good idea, because the other part of the whole fix is installing firmware, which has to be in place before the drivers will work -- but this chip is also still being used by the onboard Mac OS.
Needless to say, we can't do anything that might break his current Mac install. So anything involving firmware is not a good plan. Not only that, but I'd be doing separate drivers for every distro he wants to try.
Also, the house router is in a really inconvenient place, and without going into details, physically wiring him up via Ethernet isn't an option. If he wants networking, it has to be wifi.
So then I thought that since USB wifi dongles are cheap, we could just get him one, which would allow me to personally test it out and do whatever needs to be done on the driver side before he ever even sees it.
There's a little Netgear one that's under $40 that I have my eye on; it has to be physically tiny so he can still use the only other USB port tight up against it for the LiveUSB stick, and this fits the bill. They're handy to have, so even if he never goes full Linux we'd just keep it as a backup for ourselves. Win/win.
So here's my question for you good people. Keeping in mind he's still trying distros and has not even begun to settle on one, will a secondary USB wifi dongle allow him to test distros with wifi via LiveUSB sessions?
Are most standard USB wifi dongles supported out of the box by mainstream Linux distros?
Does anyone else have any suggestions on how to get wifi going via LiveUSB just long enough for him to try individual distros?
I would look for a dongle that specifically markets itself as being Raspberry Pi compatible. Most stuff you find will prioritize Windows, but if it's marketed to work with the Pi you know it'll have at least some level of Linux compatibility. Once you find one, try to figure out what chipset it uses, then search if it's supported by a handful of the distros you wanna try.
I believe a USB WiFi dongle will be a better idea than modifying live images of various distros, and others are already pointing you in the correct way for that, but I feel the need to correct one thing:
Okay, so maybe I can add some driver files to the LiveUSB or something? . . . nope. Not a good idea, because the other part of the whole fix is installing firmware, which has to be in place before the drivers will work -- but this chip is also still being used by the onboard Mac OS.
The WiFi module doesn't have any persistent memory for firmware, which is why the system needs to bring its own firmware - it is uploaded to the chip on every boot as part of driver initialization. So there is no risk of interfering with macOS here.
The installation in the guide refers to putting the firmware in a place where the driver will be able to find it. In other words, you would be installing the firmware on the Linux system, not onto the WiFi module.
I believe a USB WiFi dongle will be a better idea than modifying live images of various distros
Yeah, you and me both. But I'd be willing to do it for one or two, just to be able to prove that THIS laptop can and will run Linux with its current hardware, should he choose install it.
Also, the only thing lost by modifying LiveUSB trials is my time. If I corrupt the image, or it doesn't work, or I make it crap out somehow -- all of which is likely, lol -- I still have done no harm at all. It's just a USB stick. And I will also have learned a few things along the way, like how Linux distros install and use drivers.
you would be installing the firmware on the Linux system, not onto the WiFi module.
Then technically (not that I personally have the chops to do it) this "firmware" could also be something plugged into the distro on the LiveUSB stick along with the wl driver. That distro is getting its current drivers from somewhere on that USB already, so I'm not reinventing the wheel, just adding to what is already there.
I guess I just have to read up more. Thanks for letting me know the difference.
Yeah . . . that's a bit more problematic than it might seem at first glance. There are a number of USB wifi dongles that advertise Linux, but then you start reading reviews and it's actually "after I tried and discarded the manufacturer driver I used another driver for a similar chipset" etc.
It's also not something I can do on a LiveUSB trial, because you actually have to install drivers, unless I can find the correct driver files and put them on the LiveUSB directly.
If I do get the Netgear A6150 that's the process I can expect there as well, but at least it's a known-good. There's also a list on Github of supported USB wifi adapters, but those are all too big physically, more than we want to spend, or both.
It's a good thought, though. I was hoping for something so mainstream that Linux would pretend for a hot second to be plug and play, lol.
It definitely got me thinking, so thank you for your response.