On Fri, Jun 28, 2024 at 05:39:45PM +0200, Andrey Konovalov wrote: > (syzkaller to bcc) > > Hi Alan, > > I hope you could you clarify some things wrt the remote wake up > support in gadget drivers. > > Please see the Darrion's message first: > > On Fri, Jun 28, 2024 at 5:34 AM Darrion Ramos <darrionramos@xxxxxxxxx> wrote: > > > > Additionally, we have been looking into the raw_gadget and have > > noticed that the keyboard example (both a physical instance on a > > raspberry pi and the virtual instance) do not wakeup the host device > > from suspend. I don't understand the second part. With a virtual instance, the gadget is physically on the host. So if the host is suspended, how can the gadget do anything at all, let alone wake up the host? > > It seems that the emulated device does not communicate > > to the host that it is a wakeup capable device. The > > /sys/bus/devices/.../power directory for the respective udc is > > missing the wakeup files that would enable this. What you wrote here is not what you meant; there is no /sys/bus/devices/ path. Did you mean /sys/bus/usb/devices/... on the host, or did you mean /sys/bus/platform/... (or whatever) on the RPi? > > From my research on > > this I only found that the usb_gadget struct for the device needs to > > have the wakeup_capable flag set for the host to recognize the > > device as a remote wakeup source. I have printed the value during > > the gadget_bind and it seems to be set so I am not sure what else > > could be causing the host to not have the device recognized for > > remote wakeup. If anybody has any ideas on what needs to be modified > > in the raw_gadget or any resources for looking into it more it would > > be greatly appreciated, thanks! The /sys/bus/usb/devices/.../power/wakeup file on the host will generally reflect the setting of the USB_CONFIG_ATT_WAKEUP bit in the gadget's configuration descriptor bmAttributes byte. The code that sets wakeup_capable is in drivers/usb/core/hub.c, in the usb_set_device_state() function. You can see that it uses the USB_CONFIG_ATT_WAKEUP bit. > I assume that to take advantage of remote wake up, the device needs to > first of all set the USB_DEVICE_REMOTE_WAKEUP bit in bmAttributes. That bit gets set when the host tells the gadget to enable remote wakeup. And generally the UDC driver handles this, not the gadget driver. > But then, is the wake up supposed to be initiated through the gadget > driver or through the UDC sysfs files as the ones that Darrion > mentioned? The wakeup request is initiated by the gadget driver calling usb_gadget_wakeup(). > For the former case, I assume that adding a new ioctl to Raw Gadget > that calls usb_gadget_wakeup() would be a way to support this? Yes. > AFAICS, only the g_zero gadget driver calls usb_gadget_wakeup(). Do > the other gadget drivers just have no support for remote wake up? Grep shows that function/u_ether.c also calls usb_gadget_wakeup(). I don't know about most of the gadget drivers. The f_mass_storage driver has no need for remote wakeup, for example, and the same is probably true for a lot of the others. You'd think that the f_hid function would support remote wakeup, but maybe nobody ever implemented it. Alan Stern
