Dear Debian maintainers, Following my report, I tried to figure out the conditions that led to the bizarre behaviour of the scanning utilities on my Debian installation.
I tested the issue systematically on several machines (both 32 and 64 bits) running fresh installations of Debian 10.4, under gdm3, lightdm and openbox, under XFCE and GNOME, with Wayland and Xorg, with all USB-3.0 ports, a mix of USB-3.0 and USB-2.0 ports, and even an old computer with only USB-1.1 ports, through direct connections to the computers or via a port replicator. I also tried another scanner. I could not reproduce the problem (i.e. everything worked all right), except on the ThinkPad L570 (which never scanned properly with the old Canon LiDe30, but not the more recent scanner, under every tested OS environment). This led me to conclude that it had somehow to lie in the USB hub (all USB-3.0 ports) of that machine. After stumbling by chance on a hint in the MX-Linux Wiki at https://mxlinux.org/wiki/hardware/scanners, I applied the suggested fix -- which solved the problem completely. To summarize : a) Old (pre-USB-3.0) scanners may enter an USB autosuspend mode from which they cannot be awakened by the libsane back-end, nor by front-end scanning utilities such as simplescan or Xsane. b) One can configure the TLP power management by adjusting the configuration in /etc/default/tlp to disable autosuspend for the specific scanner. The line to change is (in the case of a Canon LiDe30): USB_BLACKLIST="04a9:220e" c) The parameter to add to the blacklist is first found by running lsusb, which in my case returned: Bus 001 Device 004: ID 04a9:220e Canon, Inc. CanoScan N1240U/LiDE 30 Conclusion. 1. The error report can be closed and the problem considered as solved. 2. I strongly suggest documenting the fix in the manpage for sane-usb(5). I hope this will be useful for the Debian community. Sincerely E.Casais
