> > > > With Tatyana's patches, if we load a USB2 g_zero to dummy_hcd, > enumeration > > will fail where it shouldn't. This has been my whole point ;-) Maybe > I wasn't > > clear enough. > > I guess not. I thought Tatyana said she was working to fix that bug... This bug is fixed with the module parameter. When dummy_hcd is loaded it registers 2 root hubs: HS & SS but unless the is_super_speed parameter is true, the device will be connected to the HS hub. This way when loading HS g_zero it enumerates under HS root hub successfully. Note that if load SS gadget without setting is_super_speed=true for dummy hcd, it will also enumerate under HS hub! This is basically a way to test that SS devices are backward compatible. > > >> What about the case where SuperSpeed enumeration > > >> fails and you have to fall back to high speed? > > > > > > If SuperSpeed enumeration fails, say because the device doesn't > have > > > any SuperSpeed descriptors, xhci-hcd doesn't fall back to high > speed, > > > does it? dummy-hcd should behave the same way. > > > > it should at least. Isn't that what happens between EHCI/OHCI ? HS > Chirp > > sequencing fails, then we fall back to FullSpeed. > > That's a failure in initialization, not a failure in enumeration. > > There are two reasons why the HS chirp might fail: the device doesn't > support high speed operation or hardware errors prevent the chirp from > working. With dummy-hcd there are no hardware errors (because there's > no hardware). > > As for whether or not the device supports high-speed or SuperSpeed > operation, that's determined by the usb_gadget_driver->speed field. If > the field doesn't specify SuperSpeed then dummy-hcd should connect the > gadget to the USB-2 root hub rather than the USB-3 root hub. Isn't > that what Tatyana's patch does? It contains a line saying: > > dum->gadget.speed = driver->speed; You're right. This is exactly what is done with a small update: if is_super_speed=false the gadget will connect to a USB2 root hub even if driver->speed=USB_SPEED_SUPER. In that case dum->gadget.speed will be set to USB_SPEED_HIGH. The code that sets this now is: if (mod_data.is_super_speed) dum->gadget.speed = driver->speed; else dum->gadget.speed = min((u8)USB_SPEED_HIGH, (u8)driver->speed); if (dum->gadget.speed < driver->speed) dev_dbg(udc_dev(dum), "This device can perform faster if" " you connect it to a " "SupeSpeed port...\n"); > > >> It seems like you really > > >> need to handle both speeds and the speed fall back parameter in > the same > > >> driver. Isn't there some other gadget driver that has a fall back > to > > >> full or low speed when high speed enumeration fails? > > > > > > That's a property of the gadget driver, not the UDC driver. dummy- > hcd > > > is a UDC driver (and an HCD too). > > > > USB3.0 dummy_hcd should still enumerate USB2.0 gadget drivers. > > Yes, certainly it should. If it doesn't, that's a bug, not a design > error. > This version of dummy_hcd enumerates HS devices without any issues. Best regards, Tanya Brokhman Consultant for Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
