Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756491Ab1EWQaf (ORCPT ); Mon, 23 May 2011 12:30:35 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:60937 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1756376Ab1EWQae (ORCPT ); Mon, 23 May 2011 12:30:34 -0400 Date: Mon, 23 May 2011 12:28:27 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Sarah Sharp cc: Tanya Brokhman , , , , , , "'open list'" Subject: Re: [PATCH v12 7/8] usb: Adding SuperSpeed support to dummy_hcd In-Reply-To: <20110523160803.GB5606@xanatos> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2135 Lines: 54 On Mon, 23 May 2011, Sarah Sharp wrote: > > 2. whether the device HW supports SS protocol. In our scenario it can since > > SS support is enabled in our udc. (We haven't released it yet.) > > What is a UDC? USB Device Controller. It's the device-side analog of a host controller. > > Since in dummy_hcd all of this is much simpler I think that the device speed > > should be determined by driver->speed and "which type of cable the > > connection was made over - SS or HS". The "cable type" is exactly what the > > module parameter is. > > I really don't understand this. You're going to have a module parameter > for what type of cable is plugged in? It would be more accurate to say the module parameter will be used to force the connection to run at a lower speed than the maximum possible. This is kind of like what happens when you plug in a SuperSpeed device using a USB-2 cable -- the connection runs at a lower speed than it could have. > How can you tell which one the > user is going to use? This isn't about actual cables or devices. dummy-hcd is an emulator; it presents as a host controller and a device controller both on the same system. This allows people to test gadget drivers without having any UDC hardware. > 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 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). Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/