On Tue, 16 Aug 2011 22:51:26 +0400, Andrew wrote: 

> Hello, all
> I've just patched the latest kernel to work with dwc_otg driver, thanks to
> Layne Edwards' patches.
> Everything works fine except one: I'm getting high CPU loads and
> unresponsiveness when a 3g modem is 
> plugged into a usb 2.0 hub, which, in turn, is plugged into the router.
> Bringing up ppp connection and sending AT commands back and forth on the
> second virtual ttyUSB causes
> hangups and watchdog reboots.
> Logging in via ssh is sometimes impossible when 3g is up: dropbear eats up
> about 60% CPU and does nothing. 
> Typing reboot will never reboot the system, unless you take of all usb
> devices: it just hangs bringing 
> down loopback interface. 
> Setting pti_enable module parameter to 1 helps a little, but it's still
> mostly unusable. 
> However, when I plug the modem directly in the router... Everything works
> fine, incl. proper reboots. 
> Is that likely a bug dwc_otg or just a broken hub
?(works fine on my
> desktop, though)
> I'll try to get a hub on different chipset tomorrow and post the results. 
> 
> USB descriptor dumps of the hub follow: 
> 
> necromant@ilwyn:~$ sudo lsusb -vv -s 2:10
> [sudo] password for necromant: 
> 
> Bus 002 Device 010: ID 1a40:0101 TERMINUS TECHNOLOGY INC. USB-2.0 4-Port
> HUB
> Device Descriptor:
> bLength 18
> bDescriptorType 1
> bcdUSB 2.00
> bDeviceClass 9 Hub
> bDeviceSubClass 0 Unused
> bDeviceProtocol 1 Single TT
> bMaxPacketSize0 64
> idVendor 0x1a40 TERMINUS TECHNOLOGY INC.
> idProduct 0x0101 USB-2.0 4-Port HUB
> bcdDevice 1.11
> iManufacturer 0 
> iProduct 1 USB 2.0 Hub
> iSerial 0 
> bNumConfigurations 1
> Configuration Descriptor:
> bLength 9
> bDescriptorType 2
> wTotalLength 25
> bNumInterfaces 1
> bConfigurationValue 1
> iConfiguration 0 
> bmAttributes 0xe0
> Self Powered
> Remote Wakeup
> MaxPower 100mA
> 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 12
> Hub Descriptor:
> bLength 9
> bDescriptorType 41
> nNbrPorts 4
> wHubCharacteristic 0x0000
> Ganged power switching
> Ganged overcurrent protection
> TT think time 8 FS bits
> bPwrOn2PwrGood 50 * 2 milli seconds
> bHubContrCurrent 100 milli Ampere
> DeviceRemovable 0x00
> PortPwrCtrlMask 0xff
> Hub Port Status:
> Port 1: 0000.0503 highspeed power enable connect
> Port 2: 0000.0100 power
> Port 3: 0000.0100 power
> Port 4: 0000.0100 power
> Device Qualifier (for other device speed):
> bLength 10
> bDescriptorType 6
> bcdUSB 2.00
> bDeviceClass 9 Hub
> bDeviceSubClass 0 Unused
> bDeviceProtocol 0 Full speed (or root) hub
> bMaxPacketSize0 64
>
bNumConfigurations 1
> Device Status: 0x0001
> Self Powered

Andrew, 

I haven't done much testing with the dwc otg driver and an external hub. I have 
a few hubs, and I will do some testing. I'm interested to see your results as 
well. 

Is your 3G modem perhaps an USB 1.1 device? If so, you may want to use a 
multi-TT hub for best performance. 

Regards,
Layne 
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