On Mon, 18 Mar 2019, Felipe Balbi wrote:
> Hi,
>
> Randy Dunlap <rdun...@infradead.org> writes:
> > Linux v5.0-11053-gebc551f2b8f9 of March 12, on x86_64:
> >
> > with
> > CONFIG_USB_G_DBGP=m
> > # CONFIG_USB_G_DBGP_PRINTK is not set
> > CONFIG_USB_G_DBGP_SERIAL=y
> > CONFIG_USB_U_SERIAL=m
> >
> > Loading g_dbgp module and then unloading it causes:
> >
> > WARNING: CPU: 0 PID: 24523 at
> > ../drivers/usb/gadget/function/u_serial.c:1195
> > gserial_free_line+0x161/0x2b0 [u_serial]
> >
> >
> > Is that expected?
>
> Not really, but I tried reproducing this here and couldn't get the same
> behavior. In fact, I can't see how that driver can work without a
> configuration descriptor. Here are all descriptor defined by the driver:
>
> 36:static struct usb_device_descriptor device_desc = {
> 46:static struct usb_debug_descriptor dbg_desc = {
> 51:static struct usb_endpoint_descriptor i_desc = {
> 58:static struct usb_endpoint_descriptor o_desc = {
>
> And here's an excerpt of the setup function:
>
> static int dbgp_setup(struct usb_gadget *gadget,
> const struct usb_ctrlrequest *ctrl)
> {
> struct usb_request *req = dbgp.req;
> u8 request = ctrl->bRequest;
> u16 value = le16_to_cpu(ctrl->wValue);
> u16 length = le16_to_cpu(ctrl->wLength);
> int err = -EOPNOTSUPP;
> void *data = NULL;
> u16 len = 0;
>
> if (request == USB_REQ_GET_DESCRIPTOR) {
> switch (value>>8) {
> case USB_DT_DEVICE:
> dev_dbg(&dbgp.gadget->dev, "setup: desc device\n");
> len = sizeof device_desc;
> data = &device_desc;
> device_desc.bMaxPacketSize0 = gadget->ep0->maxpacket;
> break;
> case USB_DT_DEBUG:
> dev_dbg(&dbgp.gadget->dev, "setup: desc debug\n");
> len = sizeof dbg_desc;
> data = &dbg_desc;
> break;
> default:
> goto fail;
> }
> err = 0;
> } else if (request == USB_REQ_SET_FEATURE &&
> value == USB_DEVICE_DEBUG_MODE) {
> dev_dbg(&dbgp.gadget->dev, "setup: feat debug\n");
> #ifdef CONFIG_USB_G_DBGP_PRINTK
> err = dbgp_enable_ep();
> #else
> err = dbgp_configure_endpoints(gadget);
> if (err < 0) {
> goto fail;
> }
> err = gserial_connect(dbgp.serial, tty_line);
> #endif
> if (err < 0)
> goto fail;
> } else
> goto fail;
>
> It always stalls GetDescriptor(Configuration) requests. It's also
> missing interface descriptors. What gives? How can that work?
Good questions. Has this driver ever worked?
> Anybody has a specification for how this class is supposed to work? I
> suppose this is EHCI-specific?
The file I've got is named debugdev-r090.pdf, dated 2003, and I think
it came from the usb.org web site although I can't find it there now.
Perhaps it has been updated to USB-3.1 or removed entirely. If you
would like, I can send you my copy.
The spec says:
All Debug Devices, with the exception of fixed address devices,
must implement all required standard commands in the core
device framework.
But that refers to standard _commands_, not standard _descriptors_.
The spec also says that a debug device cannot be enumerated by standard
USB-2 means, because it supports an ep0 maxpacket size of only 8 rather
than 64.
And yes, the driver is EHCI-specific -- it says so right at the start
of the file. On the other hand, I don't see any reason in theory why
it couldn't work with any other host controller that has USB high-speed
debug support.
Alan Stern
