On Fri, Dec 10, 2021 at 12:04 AM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, Dec 09, 2021 at 09:19:24AM +0800, Kai-Heng Feng wrote: > > On Thu, Dec 9, 2021 at 5:45 AM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > On Wed, Dec 08, 2021 at 03:08:33PM +0800, Kai-Heng Feng wrote: > > > > When a new USB device gets plugged to nested hubs, the affected hub, > > > > which connects to usb 2-1.4-port2, doesn't report there's any change, > > > > hence the nested hubs go back to runtime suspend like nothing happened: > > > > > > That's a bug in the hub. When there's a change in the connection status > > > of one of its ports, it should report this change to the kernel. > > > > I think it should, but when I searched through the USB spec and I > > can't find anywhere specify hub requires to report it in change > > status. > > USB-2.0 spec, section 11.24.2.7.2.1 (C_PORT_CONNECTION): > > This bit is set when the PORT_CONNECTION bit changes because of an > attach or detach detect event (see Section 7.1.7.3). This bit will be > cleared to zero by a ClearPortFeature(C_PORT_CONNECTION) request or > while the port is in the Powered-off state. It's indeed set for the hub's downstream facing port, and that's why wake up the hub and check its ports can still find connect event. But I can't find anywhere stats how hub's upstream facing port should be set. > > > > So because of this buggy hub, you now want to wake up _every_ hub in the > > > system whenever any wakeup event occurs? Is this really a good idea? > > > Is there a better way to solve the problem, such as a special quirk > > > flag? > > > > If there's no other activities, the USB hub should go back to suspend > > immediately, so the impact is minimal. > > Not immediately, but after a few seconds. However your patch will affect every > hub, not just the one that the new device was plugged into. Yes, that's the case here. > > > I've seen several similar bug reports so I think this solution should > > be applied for all hubs. > > Maybe those bug reports all had something in common, such as the type of hub or > the bus speed they were running at. Did you check? The hub in question is a SuperSpeed hub. Let me scan bug reports on Launchpad and see what I can find. Kai-Heng > > Alan Stern
