On Fri, Aug 15, 2025 at 09:13:09PM +0300, ValdikSS wrote: > I *buy* these legacy devices to improve them in Linux :) > > I'm making an open-source print server hardware for older printers, that's > why for me this issue is worth researching, at least to document such > hardware heisenbugs. > There've been different USB behavior and incompatibilities with scanners > (fixed it in SANE) and printers (fixed by CUPS quirks file), but this is the > first time I'm going down to USB HC level. > > This printer (Canon LBP1120) does not have drivers for 64-bit Windows or > recent macOS, that's why for many it's a paperweight device you can't use or > sell, unless fixed by other means (usually a VM with 32-bit Windows, and now > my print server as well). > > You gave me directions where I should look for, because I didn't know how to > start debugging without the logic analyzer. > Usbmon captures only USB communication packets and some of USB HUB > controlling packets (such as TT related), but does not include > device-controlling MMIO registers, which was the case here. > > I'll add debug prints to everything related to MMIO and take a look what > could be improved. Thanks! Good luck! > If you have other ideas I could try right away, please share them! You might compare the usbmon traces for your patched OHCI against a UHCI system. They should run at approximately the same speed, so it's not clear why the printer would work with one but not the other. Alan Stern
