On Mon, Nov 22, 2021 at 11:25:26AM -0500, David Niklas wrote: > Ok, I first edited the kernel to return -ENOMEM like you suggested but > the UPS still disconnected. I then edited it again to re-add the 1060 > byte request and the UPS still disconnected. > > I'm attaching the usbmon traces. > If you need any additional info I'll do my best to provide it. Holy cow! I just realized what's going on. And these little changes we've been messing around with have nothing to do with it. For the first time, I looked at the timestamps in the usbmon traces. It turns out that the disconnects occur several seconds after the kernel retrieves the HID report descriptor from the device. Under normal conditions we would expect to see report packets coming in from the device, starting just a fraction of a second after the descriptor is received. But that isn't happening in the Linux traces, whereas it does happen in the Windows pcap log. I would guess that the UPS is programmed to disconnect itself electronically from the USB bus if it doesn't get any requests for reports within a couple of seconds. That certainly would explain what you've been seeing. I can't imagine why it would be programmed to behave this way, but companies have been known to do stranger things. As for why the kernel doesn't try to get the reports... That's a little harder to answer. Maybe Jiri or Benjamin will know something about it. The UPS's vendor ID is 0d9f (POWERCOM) and the product ID is 0004. Now, the drivers/hid/hid-quirks.c file contains a quirk entry for 0d9f:0002 (product POWERCOM_UPS), which is probably an earlier model of the same device, or a very similar device. This quirk entry is in the hid_ignore_list; it tells the HID core not to handle the device at all. I don't know why that quirk entry is present, and furthermore, it can't directly affect what is happening with your device because the product IDs are different. Still, it is an indication that something strange is going on behind the scenes. Perhaps there is no kernel driver for these UPS devices? Perhaps the intention is that some user program will handle all the communication when one of them is detected? A quick search on Google turns up usbhid-ups, part of Network USB Tools (NUT) -- maybe you need to install that package in order to use the device. I don't know what the full story is. With luck, Jiri or Benjamin can help more. Alan Stern
