Comment 11 for bug 1826691

@You-Sheng

Sorry, our messages must have crossed paths.

Appears to be the third device from the strace of the fwupd process in the hung state.

$ grep -i drm strace.log | tail -n 2
2897 20:01:01.099170 lseek(19</dev/drm_dp_aux3>, 1200, SEEK_SET) = 1200
2897 20:01:01.099193 read(19</dev/drm_dp_aux3>, <unfinished ...>) = ?

So as you suspected, when I ran your test program I got the same hang.

sudo ./read-dpcd /dev/drm_dp_aux3

Hangs forever. Does not respond to various kill signals. Must be the caps aux_read call because there are no prints before the hang.