On Thu, 8 May 2014, Paul Zimmerman wrote: > > When the host already timed out the control transfer and started a new > > one. Here's what I'm talking about: > > > > Host sends a Set-Configuration request. > > > > The UDC driver calls the gadget driver's setup function. > > > > The setup function returns DELAYED_STATUS. > > > > After a few seconds, the host gets tired of waiting and > > sends a Get-Descriptor request > > > > The gadget driver finally submits the delayed request response > > to the Set-Configuration request. But it is now too late, > > because the host expects a response to the Get-Descriptor > > request. > > > > > dwc3 can't move to SETUP phase until the status request arrives, > > > so any SETUP transaction from host will fail. If status request > > > eventually arrives, it already missed the first control transfer, and > > > I don't know how the controller will behave. If we still can get a > > > STATUS XferComplete event without actually transfer anything on the > > > bus, then we can move back to SETUP PHASE which will remove the stale > > > delayed status request and start the new SETUP transaction. But I think > > > in this situation, the host should already lose it patience and start > > > to reset the bus. > > > > My point is that the UDC driver can't handle this. Therefore the > > gadget driver has to prevent this from happening. > > > > That means composite.c has to avoid sending delayed status responses if > > a new SETUP packet has been received already. > > > > > Per my understanding, it's impossible for dwc3 to send a stale STATUS > > > request for a new SETUP transaction. > > > > dwc3 won't know that the status response is stale. It will think the > > response was meant for the new transfer, not the old one. > > The DWC3 controller will actually handle this case on its own. If > it sees another SETUP packet come in before the previous Control > transfer has completed, it will not send any DATA or STATUS phase > packets for the previous Control transfer to the host. But it will > "fake" the correct responses to the software, so the dwc3 driver will > think that the DATA/STATUS stages completed successfully, even though > nothing actually went out on the bus. That doesn't handle the problem I described above. When the dwc3 driver gets the late delayed status response, it will think it is a response to the new SETUP packet, and so it will carry out a bogus transfer. It won't know that the status request was meant to be a response to a defunct control transfer. > For other controllers that can't do this, maybe it should be handled > in the UDC driver rather than in the composite gadget? The only place this can be handled properly is in the gadget driver: composite.c for those gadgets using it, otherwise in the higher level driver (if there are any remaining gadgets that don't use the composite framework). Alan Stern -- 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
