On Tue, Jan 25, 2022 at 02:09:18PM +0100, Sven Schnelle wrote: > Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes: > > > Now the documentation states we need this super speed A<->A cable, but > > could you also update the documentation for usb-c ? There's a fair > > number of usb-c only devices out there now. > > Stupid beginners question: Would every USB3 A-A cable work, or are the > debug cables special? I've read the RX/TX pairs have to be swapped, but > to me it looks like that's always the case? I'm using a random USB3 A-A cable (it came with an HDMI frame grabber of of AliExpress). The official one has a wire missing I think, to avoid ground loops or something like that. The easiest thing to do is try the runtime DBC option: echo enable > /sys/bus/pci/devices/0000:00:14.0/dbc If that works you can see what it takes to make the earlyprintk one working. This thread seems to have much of that covered.
