On Sat, 27 Jun 2015, Greg Kroah-Hartman wrote:
> On Fri, Jun 26, 2015 at 09:20:19PM -0400, Alan Stern wrote:
> > My Apple keyboard isn't here at the moment, and I don't remember
> > exactly what its hub descriptor contains. In theory, it _should_ mark
> > the permanently attached port as non-removable.
> >
> > I can test it next week, if you would like to see the actual values.
>
> That would be great.
Here we go:
# lsusb -v -s 3:4
Bus 003 Device 004: ID 05ac:1002 Apple, Inc. Extended Keyboard Hub [Mitsumi]
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 1.10
bDeviceClass 9 Hub
bDeviceSubClass 0 Unused
bDeviceProtocol 0 Full speed (or root) hub
bMaxPacketSize0 8
idVendor 0x05ac Apple, Inc.
idProduct 0x1002 Extended Keyboard Hub [Mitsumi]
bcdDevice 1.22
iManufacturer 1 Mitsumi Electric
iProduct 2 Hub in Apple Extended USB Keyboard
iSerial 0
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 25
bNumInterfaces 1
bConfigurationValue 1
iConfiguration 0
bmAttributes 0xa0
(Bus Powered)
Remote Wakeup
MaxPower 50mA
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 1
bInterfaceClass 9 Hub
bInterfaceSubClass 0 Unused
bInterfaceProtocol 0 Full speed (or root) hub
iInterface 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0001 1x 1 bytes
bInterval 255
Hub Descriptor:
bLength 9
bDescriptorType 41
nNbrPorts 3
wHubCharacteristic 0x0004
Ganged power switching
Compound device
Ganged overcurrent protection
bPwrOn2PwrGood 22 * 2 milli seconds
bHubContrCurrent 50 milli Ampere
DeviceRemovable 0x02
PortPwrCtrlMask 0xff
Hub Port Status:
Port 1: 0000.0103 power enable connect
Port 2: 0000.0100 power
Port 3: 0000.0100 power
Device Status: 0x0000
(Bus Powered)
As you can see, the hub descriptor says that the hub is part of a
compound device. Port 1 is attached to the internal keyboard
controller, so it is connected and enabled, whereas the other two ports
don't have anything plugged in right now.
Most importantly, the DeviceRemovable bitmask is set to 0x02. Since
bit 0 is reserved, the bit that is set corresponds to port 1. It is
set to indicate that the port is non-removable (i.e., the meaning is
the opposite of what the name suggests). And sure enough:
$ cat /sys/bus/usb/devices/3-1.4.1/removable
fixed
(The internal hub is 3-1.4, and the keyboard controller is therefore
3-1.4.1.)
I don't have any computers with a device permanently attached to an
xHCI root-hub port. If someone else does, maybe they can check what
happens when these two lines:
if (!(wHubCharacteristics & HUB_CHAR_COMPOUND))
return;
are deleted from drivers/usb/core/hub.c:set_usb_port_removable().
Deleting those lines may cause the device to show up as "fixed" rather
than "removable".
Alan Stern
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