That looks like a reasonable question (about that line) to the dev list.
Although there might be info on www.usb.org about this.

On Wed, 10 Mar 2004, Malcolm Blaney wrote:

> Hi all,
>
> I'm happy to say usb no longer hangs on my single board computer! I
> thought I'd try diffing the uhci code from the kernel we had working,
> (2.4.18) and kernels that don't (so far 2.4.23 and 2.4.24). I got down
> to _one_ line causing the problem:
>
> uhci->fsbr = 0;   ...in alloc_uhci().
>
> Which was of course added in 2.4.19. I removed the line, since it's not
> in 2.4.18, and all the devices I had trouble with worked. Is this worth
> posting to the dev list? Can someone tell me the effect of setting fsbr
> to 0?
>
> Guennadi Liakhovetski wrote:
>  > Sorry, I have very little time these days, I will have a better look
>  > at your debugging output, but meanwhile - do you have a chance to
>  > up/downgrade the BIOS on your non-working 600MHz system to the 400MHz
>  > state?
> That's been tried, and we killed a 600MHz board in the process! We asked
> the board producer (Boser) to do it for us as well, but didn't hear much
> back from them...
>
> Unfourtunately though, my problems haven't gone away. the usb bandwidth
> isn't high enough for what we want to do, it seems to be stopping and
> starting when trying to do bulk transfers. And since 'full speed
> bandwidth reclamation' was causing my problems before, it sounds related
> to me.
>
> I'll try and produce some decent data to show that it's slow, but in the
> mean time here is the dmesg and /proc/bus/usb/devices output of our
> running (but slow) system:
>
> dmesg:
> hub.c: new USB device 00:07.2-1, assigned address 7
> usb.c: kmalloc IF ce747700, numif 1
> usb.c: new device strings: Mfr=1, Product=2, SerialNumber=0
> usb.c: USB device number 7 default language ID 0x409
> Manufacturer: Texas Instruments, Inc.
> Product: TMX320VC5509
> usb.c: unhandled interfaces on device
> usb.c: USB device 7 (vend/prod 0x451/0x9001) is not claimed by any
> active driver.
>    Length              = 18
>    DescriptorType      = 01
>    USB version         = 1.01
>    Vendor:Product      = 0451:9001
>    MaxPacketSize0      = 64
>    NumConfigurations   = 1
>    Device version      = 0.00
>    Device Class:SubClass:Protocol = 00:00:00
>      Per-interface classes
> Configuration:
>    bLength             =    9
>    bDescriptorType     =   02
>    wTotalLength        = 0019
>    bNumInterfaces      =   01
>    bConfigurationValue =   01
>    iConfiguration      =   03
>    bmAttributes        =   c0
>    MaxPower            =    0mA
>
>    Interface: 0
>    Alternate Setting:  0
>      bLength             =    9
>      bDescriptorType     =   04
>      bInterfaceNumber    =   00
>      bAlternateSetting   =   00
>      bNumEndpoints       =   01
>      bInterface Class:SubClass:Protocol =   00:00:00
>      iInterface          =   04
>      Endpoint:
>        bLength             =    7
>        bDescriptorType     =   05
>        bEndpointAddress    =   81 (in)
>        bmAttributes        =   02 (Bulk)
>        wMaxPacketSize      = 0040
>        bInterval           =   00
> usb.c: kusbd: /sbin/hotplug add 7
> hub.c: port 2, portstatus 300, change 0, 1.5 Mb/s
> hub.c: port 1, portstatus 103, change 0, 12 Mb/s
> hub.c: port 2, portstatus 300, change 0, 1.5 Mb/s
> usb.c: usbdevfs driver claimed interface ce747700
> uhci.c: root-hub INT complete: port1: 48a port2: 580 data: 2
> uhci.c: c400: suspend_hc
> uhci.c: root-hub INT complete: port1: 48a port2: 580 data: 2
> uhci.c: root-hub INT complete: port1: 48a port2: 580 data: 2
> hub.c: port 1, portstatus 100, change 3, 12 Mb/s
> hub.c: port 1 connection change
> hub.c: port 1, portstatus 100, change 3, 12 Mb/s
> usb.c: USB disconnect on device 00:07.2-1 address 7
> usb.c: kusbd: /sbin/hotplug remove 7
> uhci.c: root-hub INT complete: port1: 488 port2: 580 data: 2
> hub.c: port 2, portstatus 300, change 0, 1.5 Mb/s
> hub.c: port 1, portstatus 100, change 2, 12 Mb/s
> hub.c: port 1 enable change, status 100
> hub.c: port 2, portstatus 300, change 0, 1.5 Mb/s
>
> /proc/bus/usb/devices:
> T:  Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=12  MxCh= 2
> B:  Alloc=  0/900 us ( 0%), #Int=  0, #Iso=  0
> D:  Ver= 1.00 Cls=09(hub  ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
> P:  Vendor=0000 ProdID=0000 Rev= 0.00
> S:  Product=USB UHCI-alt Root Hub
> S:  SerialNumber=c400
> C:* #Ifs= 1 Cfg#= 1 Atr=40 MxPwr=  0mA
> I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
> E:  Ad=81(I) Atr=03(Int.) MxPS=   8 Ivl=255ms
> T:  Bus=01 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  9 Spd=12  MxCh= 0
> D:  Ver= 1.01 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
> P:  Vendor=0451 ProdID=9001 Rev= 0.00
> S:  Manufacturer=Texas Instruments, Inc.
> S:  Product=TMX320VC5509
> C:* #Ifs= 1 Cfg#= 1 Atr=c0 MxPwr=  0mA
> I:  If#= 0 Alt= 0 #EPs= 1 Cls=00(>ifc ) Sub=00 Prot=00 Driver=usbdevfs
> E:  Ad=81(I) Atr=02(Bulk) MxPS=  64 Ivl=0ms
>
>
>
> Thanks,
> Malcolm.
>
>
>
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