Better explanation of `upload -d`

[AndydeCleyre]

Hi, thanks for this!

upload -d is explained as

Use data flash from a file.

But it seems that without -d, with or without -e or -u, the upload command always uses a file, so it's unclear what the difference is.

Also, while I have a firmware image to upload, I don't know if it's encrypted or not. Is there a simple way to determine that?

Thanks for any help.