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From: Felipe Balbi <felipe.balbi@linux.intel.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Lu Baolu <baolu.lu@linux.intel.com>
Cc: "'Mathias Nyman'" <mathias.nyman@linux.intel.com>,
        "linux-usb\@vger.kernel.org" <linux-usb@vger.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 2/3] usb: xhci: Add DbC support in xHCI driver
In-Reply-To: <20171103062702.GB16958@kroah.com>
References: <1504576740-11689-1-git-send-email-baolu.lu@linux.intel.com> <1504576740-11689-3-git-send-email-baolu.lu@linux.intel.com> <59FA76AA.4060602@linux.intel.com> <20171102081720.GA3298@kroah.com> <871slhvy68.fsf@linux.intel.com> <20171102093216.GA16369@kroah.com> <87y3npufr2.fsf@linux.intel.com> <20171102165113.GB18566@kroah.com> <59FBBC3A.3040809@linux.intel.com> <20171103062702.GB16958@kroah.com>
Date: Fri, 03 Nov 2017 12:52:43 +0200
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Hi,

Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:
>> >>>> > >> Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:
>> >>>>>>> > >> >> > xHCI compatible USB host controllers(i.e. super-speed =
USB3 controllers)
>> >>>>>>> > >> >> > can be implemented with the Debug Capability(DbC). It =
presents a debug
>> >>>>>>> > >> >> > device which is fully compliant with the USB framework=
 and provides the
>> >>>>>>> > >> >> > equivalent of a very high performance full-duplex seri=
al link. The debug
>> >>>>>>> > >> >> > capability operation model and registers interface are=
 defined in 7.6.8
>> >>>>>>> > >> >> > of the xHCI specification, revision 1.1.
>> >>>>>>> > >> >> >
>> >>>>>>> > >> >> > The DbC debug device shares a root port with the xHCI =
host. By default,
>> >>>>>>> > >> >> > the debug capability is disabled and the root port is =
assigned to xHCI.
>> >>>>>>> > >> >> > When the DbC is enabled, the root port will be assigne=
d to the DbC debug
>> >>>>>>> > >> >> > device, and the xHCI sees nothing on this port. This i=
mplementation uses
>> >>>>>>> > >> >> > a sysfs node named <dbc> under the xHCI device to mana=
ge the enabling
>> >>>>>>> > >> >> > and disabling of the debug capability.
>> >>>>>>> > >> >> >
>> >>>>>>> > >> >> > When the debug capability is enabled, it will present =
a debug device
>> >>>>>>> > >> >> > through the debug port. This debug device is fully com=
pliant with the
>> >>>>>>> > >> >> > USB3 framework, and it can be enumerated by a debug ho=
st on the other
>> >>>>>>> > >> >> > end of the USB link. As soon as the debug device is co=
nfigured, a TTY
>> >>>>>>> > >> >> > serial device named /dev/ttyDBC0 will be created.
>> >>>>>>> > >> >> >
>> >>>>>>> > >> >> > One use of this link is running a login service on the=
 debug target.
>> >>>>>>> > >> >> > Hence it can be remote accessed by a debug host. Anoth=
er use case can
>> >>>>>>> > >> >> > probably be found in servers. It provides a peer-to-pe=
er USB link
>> >>>>>>> > >> >> > between two host-only machines. This provides a reason=
able out-of-band
>> >>>>>>> > >> >> > communication method between two servers.
>> >>>>>>> > >> >> >
>> >>>>>>> > >> >> > Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> >>>>>>> > >> >> > ---
>> >>>>>>> > >> >> >  .../ABI/testing/sysfs-bus-pci-drivers-xhci_hcd     | =
  25 +
>> >>>>>>> > >> >> >  drivers/usb/host/Kconfig                           | =
   9 +
>> >>>>>>> > >> >> >  drivers/usb/host/Makefile                          | =
   5 +
>> >>>>>>> > >> >> >  drivers/usb/host/xhci-dbgcap.c                     | =
1016 ++++++++++++++++++++
>> >>>>>>> > >> >> >  drivers/usb/host/xhci-dbgcap.h                     | =
 247 +++++
>> >>>>>>> > >> >> >  drivers/usb/host/xhci-dbgtty.c                     | =
 586 +++++++++++
>> >>>>>>> > >> >> >  drivers/usb/host/xhci-trace.h                      | =
  60 ++
>> >>>>>>> > >> >> >  drivers/usb/host/xhci.c                            | =
  10 +
>> >>>>>>> > >> >> >  drivers/usb/host/xhci.h                            | =
   1 +
>> >>>>>>> > >> >> >  9 files changed, 1959 insertions(+)
>> >>>>>>> > >> >> >  create mode 100644 Documentation/ABI/testing/sysfs-bu=
s-pci-drivers-xhci_hcd
>> >>>>>>> > >> >> >  create mode 100644 drivers/usb/host/xhci-dbgcap.c
>> >>>>>>> > >> >> >  create mode 100644 drivers/usb/host/xhci-dbgcap.h
>> >>>>>>> > >> >> >  create mode 100644 drivers/usb/host/xhci-dbgtty.c
>> >>>>>>> > >> >> >
>> >>>>>> > >> >>=20
>> >>>>>> > >> >> [snip]
>> >>>>>> > >> >>=20
>> >>>>>>> > >> >> > +#define DBC_VENDOR_ID			0x1d6b	/* Linux Foundation 0x=
1d6b */
>> >>>>>>> > >> >> > +#define DBC_PRODUCT_ID			0x0004	/* device 0004 */
>> >>>>>>> > >> >> >
>> >>>>>> > >> >>=20
>> >>>>>> > >> >> The DbC (xHCI DeBug Capability) is an optional functional=
ity in
>> >>>>>> > >> >> some xHCI host controllers. It will present a super-speed=
 debug
>> >>>>>> > >> >> device through the debug port after it is enabled.
>> >>>>>> > >> >>=20
>> >>>>>> > >> >> The DbC register set defines an interface for system soft=
ware
>> >>>>>> > >> >> to specify the vendor id and product id of the debug devi=
ce.
>> >>>>>> > >> >> These two values will be presented by the debug device in=
 its
>> >>>>>> > >> >> device descriptor idVendor and idProduct fields.
>> >>>>>> > >> >>=20
>> >>>>>> > >> >> Microsoft Windows have a well established protocol for
>> >>>>>> > >> >> debugging over DbC. And it assigns below values for its u=
se.
>> >>>>>> > >> >>=20
>> >>>>>> > >> >> USB\VID_045E&PID_062D.DeviceDesc=3D"Microsoft USB Debug T=
arget"
>> >>>>>> > >> >>=20
>> >>>>>> > >> >> I'm going to use 0x1d6b/0x0004 value pair for DbC use in
>> >>>>>> > >> >> Linux. Do you approve me to do so?
>> >>>>> > >> >
>> >>>>> > >> > No.  Why can't you use the same ids as Windows?  This is im=
plementing
>> >>>>> > >> > the same protocol, right?
>> >>>> > >>=20
>> >>>> > >> the protocol running on top is 100% vendor specific. More than=
 likely,
>> >>>> > >> we would just run kgdb on top of this, right? We really don't =
support
>> >>>> > >> microsoft's debug architecture.
>> >>> > >
>> >>> > > Ah, I didn't know about the protocol specifics here, if it is
>> >>> > > vendor-specific, then yes, we need our own id.
>> >> >=20
>> >> > Great, thanks :-)
>> >> >=20
>> >> > Let us know which one we're allowed to use and I'm sure Baolu can r=
espin
>> >> > the patch in no time.
>> > Can I get a "full" description of what string this device id will
>> > reference?  Is it "Linux USB Debug Target" or something else?
>> >
>>=20
>> Current manufacturer and product strings are set like this.
>>=20
>> +#define DBC_STRING_MANUFACTURER	"Linux"
>> +#define DBC_STRING_PRODUCT		"Remote	GDB"
>>=20
>> These are also place holders. We can change them to more meaningful stri=
ngs.
>
> As the vendor id is assigned to "Linux Foundation" can we change that
> string please?
>
> And why not match what Microsoft does here, "USB Debug Target" makes
> more sense than "Remote GDB", right?

I agree. It just happens to talk remote GDB protocol through KGDB, but
we could run KDB directly or, even, come up with a new protocol.

> If so, please use device id 0x0010, I've reserved that for the driver
> now.

thanks Greg

=2D-=20
balbi

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