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    SubjectRe: [Bug #10713] ehci splatter in 2.6.26-rc2
    On Tue, May 20, 2008 at 01:11:26AM +0200, Lennert Buytenhek wrote:

    > > This message has been generated automatically as a part of a report
    > > of recent regressions.
    > >
    > > The following bug entry is on the current list of known regressions
    > > from 2.6.25. Please verify if it still should be listed.
    > >
    > >
    > > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=10713
    > > Subject : ehci splatter in 2.6.26-rc2
    > > Submitter : Lennert Buytenhek <buytenh@wantstofly.org>
    > > Date : 2008-05-14 11:24 (5 days old)
    > > References : http://marc.info/?l=linux-kernel&amp;m=121076435420129&amp;w=4
    > > Handled-By : David Brownell <david-b@pacbell.net>
    >
    > Just re-checked, and this device (a USB to dual PS/2 cable) works
    > fine on 2.6.25 on this hardware:
    >
    > usb 1-1: new low speed USB device using orion-ehci and address 2
    > usb 1-1: configuration #1 chosen from 1 choice
    > input: PS2 to USB AdapterA3 as /class/input/input0
    > input: USB HID v1.10 Keyboard [PS2 to USB AdapterA3] on usb-orion-ehci.0-1
    > input: PS2 to USB AdapterA3 as /class/input/input1
    > input: USB HID v1.10 Mouse [PS2 to USB AdapterA3] on usb-orion-ehci.0-1
    >
    > But on 2.6.26-rc3 it just gives me:
    >
    > usb 1-1: new low speed USB device using orion-ehci and address 2
    > Unable to handle kernel NULL pointer dereference at virtual address 00000000
    > pgd = c0004000
    > [00000000] *pgd=00000000
    > Internal error: Oops: 5 [#1] PREEMPT
    > Modules linked in:
    > CPU: 0 Not tainted (2.6.26-rc3 #347)
    > PC is at qh_append_tds+0x24c/0x47c
    > LR is at ehci_qtd_alloc+0x30/0x5c
    > pc : [<c0242374>] lr : [<c0241d48>] psr: 00000093
    > sp : c7cfdcb0 ip : c7e3c4c0 fp : c7cfdcfc
    > r10: ffc83080 r9 : 00000008 r8 : c7d12240
    > r7 : 80000080 r6 : 00000080 r5 : 00000000 r4 : 00000002
    > r3 : c7d3f000 r2 : 00000000 r1 : 40800000 r0 : 08085000
    > Flags: nzcv IRQs off FIQs on Mode SVC_32 ISA ARM Segment kernel
    > Control: 0005317f Table: 00004000 DAC: 00000017
    > Process khubd (pid: 79, stack limit = 0xc7cfc268)
    > Stack: (0xc7cfdcb0 to 0xc7cfe000)
    > [...]
    > Backtrace:
    > [<c0242128>] (qh_append_tds+0x0/0x47c) from [<c0243ca0>] (ehci_urb_enqueue+0x100/0xff4)
    > [<c0243ba0>] (ehci_urb_enqueue+0x0/0xff4) from [<c0234c30>] (usb_hcd_submit_urb+0x824/0x91c)
    > [<c023440c>] (usb_hcd_submit_urb+0x0/0x91c) from [<c0235098>] (usb_submit_urb+0x224/0x260)
    > [<c0234e74>] (usb_submit_urb+0x0/0x260) from [<c0235b5c>] (usb_start_wait_urb+0x44/0xac)
    > r6:c7d12240 r5:c7cfde80 r4:00000000
    > [<c0235b18>] (usb_start_wait_urb+0x0/0xac) from [<c0235dac>] (usb_control_msg+0xc8/0xec)
    > r8:00000000 r7:00000100 r6:fffffff4 r5:00000040 r4:c7e3dc20
    > [<c0235ce4>] (usb_control_msg+0x0/0xec) from [<c0230854>] (hub_port_init+0x274/0x5e4)
    > [<c02305e0>] (hub_port_init+0x0/0x5e4) from [<c0231bec>] (hub_thread+0x608/0xc10)
    > [<c02315e4>] (hub_thread+0x0/0xc10) from [<c0059e20>] (kthread+0x5c/0x94)
    > [<c0059dc4>] (kthread+0x0/0x94) from [<c0047908>] (do_exit+0x0/0x67c)
    > r6:00000000 r5:00000000 r4:00000000
    > Code: e51bc040 e5932000 e51c309c e1520003 (15923000)
    > ---[ end trace ce1992535f2e8e4d ]---
    > note: khubd[79] exited with preempt_count 1
    >
    > If you have no idea what might have caused this to creep in, I guess
    > I'll have to bisect it?

    A bisect turns up this:

    7329e211b987a493cbcfca0e98c60eb108ab42df is first bad commit
    commit 7329e211b987a493cbcfca0e98c60eb108ab42df
    Author: Alan Stern <stern@rowland.harvard.edu>
    Date: Thu Apr 3 18:02:56 2008 -0400

    USB: root hubs don't lie about their number of TTs

    Currently EHCI root hubs enumerate with a bDeviceProtocol code
    indicating that they possess a Transaction Translator. However the
    vast majority of controllers do not; they rely on a companion
    controller to handle full- and low-speed communications. This patch
    (as1064) changes the root-hub device descriptor to match the actual
    situation.

    Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    And indeed, reverting this commit from 2.6.26-rc3 makes my system
    stop oopsing when I plug in the USB-PS/2 adapter (a low speed device),
    and makes it work again as it did in 2.6.25.

    Any other info I can provide or tests I can run?


    thanks,
    Lennert


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