I'm generalising from experience of 15 to 20 vendors, of whom only a couple had their drivers upstreamed. The remainder simply did not understand why (to use some examples) I didn't want to use their vendor- specific DVB-T tuning interface instead of Linux's DVB API, or their vendor-specific video capture interface instead of V4L2.
However, I recognise that my experience may be atypical; I therefore mention that I base this on personal experience, so that if I've just had bad luck with vendors, other people can point out vendors who get it right.
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