1

If not, then why is the USB plug configured to ask to access data, which is typically the case?

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2
  • Is this USB port part of an in-flight entertainment system, or something that's purely meant as a dumb charger?
    – TooTea
    Mar 22 '21 at 9:33
  • @TooTea idk, how can I check? From what I recall, I've been asked to access data even for isolated USB ports. Mar 22 '21 at 9:49
9

Occasionally useful, mostly irrelevant.

Some in-flight entertainment systems have USB ports that let you connect your own device and then play your own movies from said device on the IFE screen. Allowing access to your files would thus be necessary to be able to browse them through the IFE system.

More often, there is no such feature and the USB port is purely meant to be used as a charger. For reasons like supporting proper current negotiation (necessary for various fast charging protocols), the USB port might not be completely dumb (having just the power lines like a wall wart charger) but actually be a valid USB device with working data lines.

Any time you connect your phone to a real USB device, it pops up the dialog asking you whether you want to actually present the file access protocols to the device or to just play dead. The device does not need to "ask to access data" first, the phone asks you before it even offers the data access features to the device.

5
  • Thanks! " The device does not need to "ask to access data" first, the phone asks you before it even offers the data access features to the device." -> why doesn't the phone ask when it is plugged to a portable phone charger via USB cable? Mar 22 '21 at 10:02
  • 2
    @FranckDernoncourt Because that's a dumb charger that does not present itself as a real USB host/device.
    – TooTea
    Mar 22 '21 at 10:03
  • Got it, thanks! Mar 22 '21 at 10:03
  • 2
    (At least that's the way my phone works. I'm just speculating that your one works the same way. When I connect my phone to my laptop, I get the USB mode selection popup even if the laptop is logged out and nothing is interested in asking the phone for any access.)
    – TooTea
    Mar 22 '21 at 10:07
  • 2
    The keyword (I strongly suspect) is that the popup comes when the phone enumerates. This is the first step of being recognised by non-dumb hardware, including a few chargers by the sound of things Mar 22 '21 at 17:00

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