On Sat, Aug 29, 2020 at 11:50:03AM +0200, Salvatore Bonaccorso wrote: > Hi Alan, > > I'm following up on this thread because a user in Debian (Dirk, Cc'ed) > as well encountered the same/similar issue: > > On Tue, Jul 21, 2020 at 10:33:25AM -0400, Alan Stern wrote: > > On Tue, Jul 21, 2020 at 07:59:17AM +0200, Michal Hocko wrote: > > > > Sorry, my mistake. The module name needs to be "xhci_hcd" with an '_' > > > > character, not a '-' character -- the same as what shows up in the lsmod > > > > output. > > > > > > > > > [14766.973734] xhci_hcd 0000:00:14.0: Get port status 2-1 read: 0xe000088, return 0x88 > > > [14766.973738] xhci_hcd 0000:00:14.0: Get port status 2-2 read: 0xe000088, return 0x88 > > > [14766.973742] xhci_hcd 0000:00:14.0: Get port status 2-3 read: 0xe0002a0, return 0x2a0 > > > [14766.973746] xhci_hcd 0000:00:14.0: Get port status 2-4 read: 0xe0002a0, return 0x2a0 > > > [14766.973750] xhci_hcd 0000:00:14.0: Get port status 2-5 read: 0xe0002a0, return 0x2a0 > > > [14766.973754] xhci_hcd 0000:00:14.0: Get port status 2-6 read: 0xe0002a0, return 0x2a0 > > > [14766.973759] xhci_hcd 0000:00:14.0: Get port status 2-1 read: 0xe000088, return 0x88 > > > [14766.973763] xhci_hcd 0000:00:14.0: Get port status 2-2 read: 0xe000088, return 0x88 > > > > According to the xHCI specification, those 02a0 values are normal and > > the 0088 values indicate the port is disabled and has an over-current > > condition. I don't know about the e000 bits in the upper part of the > > word; according to my copy of the spec those bits should be 0. > > > > If your machine has only two physical SuperSpeed (USB-3) ports then > > perhaps the other four ports are internally wired in a way that creates > > a permanent over-current indication. > > > > > [14766.973771] xhci_hcd 0000:00:14.0: set port remote wake mask, actual port 0 status = 0xe000088 > > > [14766.973780] xhci_hcd 0000:00:14.0: set port remote wake mask, actual port 1 status = 0xe000088 > > > [14766.973789] xhci_hcd 0000:00:14.0: set port remote wake mask, actual port 2 status = 0xe0002a0 > > > [14766.973798] xhci_hcd 0000:00:14.0: set port remote wake mask, actual port 3 status = 0xe0002a0 > > > [14766.973807] xhci_hcd 0000:00:14.0: set port remote wake mask, actual port 4 status = 0xe0002a0 > > > [14766.973816] xhci_hcd 0000:00:14.0: set port remote wake mask, actual port 5 status = 0xe0002a0 > > > [14766.973830] xhci_hcd 0000:00:14.0: Bus suspend bailout, port over-current detected > > > > > > Repeating again and again. The last message suggests a HW problem? But > > > why does the kernel try the same thing over and over? > > > > Because over-current is supposed to be a transient condition that goes > > away quickly. It means there's a short circuit or something similar. > > Dirk exprienced the same issue aand enabled dynamic debugging showed > similar pattern. His dmesg excerpt is attached. > > The Debian report is at https://bugs.debian.org/966703 > > What could be tracked down is that the issue is uncovered since > e9fb08d617bf ("xhci: prevent bus suspend if a roothub port detected a > over-current condition") which was applied in 5.7-rc3 and backported > to several stable releases (v5.6.8, v5.4.36 and v4.19.119). > > Dirk found additionally: > > > I just found out, that if none of the two USB ports is connected, there > > are two kworker processes with permanently high CPU load, if one USB > > port is connected and the other not, there is one such kworker process, > > and if both USB ports are connected, there is no kworker process with > > high CPU load. > > I think, this supports your suspicion that these kworker processes are > > connected with the overcurrent condition for both USB ports that I also > > see in the dmesg output. > > Reverting the above commit covers the problem again. But I'm not > exprienced enough here to claim if this is a HW issue or if the Kernel > should handle the situation otherwise. Is there anything else Dirk can > provide? It is undoubtedly a hardware issue. The dmesg extract shows that ports 1-10, 1-11, and 2-5 (which is probably the same port as one of the others) have overcurrent conditions; I'm guessing that these are the ports which have external connections. What were the devices Dirk plugged in that got rid of the kworker processes? In particular, were they USB-2 or USB-3? (The dmesg log for when the devices were first attached can answer these questions.) As far as I know, there is no way for the kernel to work around this problem. Preventing the controller from going into runtime suspend is probably the best solution. Perhaps Mathias (the xhci-hcd maintainer) will have more suggestions. Alan Stern
