Some alternate interface settings have no endpoints associated with them. This shows up in some USB webcams, particularly the Logitech HD 1080p, which uses the uvcvideo driver. If a driver switches between two alt settings with no endpoints, there is no need to issue a configure endpoint command, because there is no endpoint information to update. The only time a configure endpoint command with just the add slot flag set makes sense is when the driver is updating hub characteristics in the slot context. However, that code never calls xhci_check_bandwidth, so we should be safe not issuing a command if only the slot context add flag is set. Signed-off-by: Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx> --- drivers/usb/host/xhci.c | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-) diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c index f647d91..fcc5821 100644 --- a/drivers/usb/host/xhci.c +++ b/drivers/usb/host/xhci.c @@ -1888,6 +1888,12 @@ int xhci_check_bandwidth(struct usb_hcd *hcd, struct usb_device *udev) ctrl_ctx->add_flags |= cpu_to_le32(SLOT_FLAG); ctrl_ctx->add_flags &= cpu_to_le32(~EP0_FLAG); ctrl_ctx->drop_flags &= cpu_to_le32(~(SLOT_FLAG | EP0_FLAG)); + + /* Don't issue the command if there's no endpoints to update. */ + if (ctrl_ctx->add_flags == cpu_to_le32(SLOT_FLAG) && + ctrl_ctx->drop_flags == 0) + return 0; + xhci_dbg(xhci, "New Input Control Context:\n"); slot_ctx = xhci_get_slot_ctx(xhci, virt_dev->in_ctx); xhci_dbg_ctx(xhci, virt_dev->in_ctx, -- 1.7.4.1 -- 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
