Hi, Alan, On Fri, Jan 31, 2025 at 11:17 PM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Fri, Jan 31, 2025 at 06:06:30PM +0800, Huacai Chen wrote: > > Now we only enable the remote wakeup function for the USB wakeup source > > itself at usb_port_suspend(). But on pre-XHCI controllers this is not > > enough to enable the S3 wakeup function for USB keyboards, > > Why do you say this? It was enough on my system with an EHCI/UHCI > controller when I wrote that code. What hardware do you have that isn't > working? > > > so we also > > enable the root_hub's remote wakeup (and disable it on error). Frankly > > this is unnecessary for XHCI, but enable it unconditionally make code > > simple and seems harmless. > > This does not make sense. For hubs (including root hubs), enabling > remote wakeup means that the hub will generate a wakeup request when > there is a connect, disconnect, or over-current change. That's not what > you want to do, is it? And it has nothing to do with how the hub > handles wakeup requests received from downstream devices. > > You need to explain what's going on here in much more detail. What > exactly is going wrong, and why? What is the hardware actually doing, > as compared to what we expect it to do? OK, let me tell a long story: At first, someone reported that on Loongson platform we cannot wake up S3 with a USB keyboard, but no problem on x86. At that time we thought this was a platform-specific problem. After that we have done many experiments, then we found that if the keyboard is connected to a XHCI controller, it can wake up, but cannot wake up if it is connected to a non-XHCI controller, no matter on x86 or on Loongson. We are not familiar with USB protocol, this is just observed from experiments. You are probably right that enabling remote wakeup on a hub means it can generate wakeup requests rather than forward downstream devices' requests. But from experiments we found that if we enable the "wakeup" knob of the root_hub via sysfs, then a keyboard becomes able to wake up S3 (for non-XHCI controllers). So we guess that the enablement also enables forwarding. So maybe this is an implementation-specific problem (but most implementations have problems)? This patch itself just emulates the enablement of root_hub's remote wakeup automatically (then we needn't operate on sysfs). Huacai > > Alan Stern
