Re: How to safe recover USB driver from broken hardware situation

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On Mon, Apr 22, 2013 at 11:26:05AM -0400, Alan Stern wrote:
> On Mon, 22 Apr 2013, Peter Chen wrote:
> 
> > Hi all,
> > 
> > Recently, I have several customers troubled in safe recover USB
> > function during the ESD situation (or some other situations, like
> > short dp/dm, ground dp/dm, etc).
> > 
> > I designed the ESD detect and recovery process, but I met some
> > sync problems between host controller driver (eg, ehci) and class
> > driver (eg, mass storage). For example, when khubd tries to disconnect
> > usb device, it will try to stop thread usb-storage, but usb-storage
> > is waiting some transfers to finish, qTD and QH operation may be 
> > finished (usb_submit_urb does not return error), but no watchdog timer
> > and completion interrupt are occurred.
> > 
> > I have:
> > esd_detect_process and esd_recovery_process at host controller driver.
> > At esd_detect_porcess
> > It will disable usb interrupt and judge ASE and PSE, etc.
> > At esd_recovery_process:
> > It needs to reset controller (usbcmd.rst, and toggle portsc.pp bit, etc)
> > 
> > I would like to have some synchronization mechanism between usb_submit_urb
> > or (ehci_urb_enqueue) and my esd_detect_process and esd_recovery_process.
> > But still not find a safe one, eg, I still met khubd's status changes 
> > "D" problem described above. Any suggestions are appreciated, Thanks.
> 
> Your recovery process should not need to make all these changes to
> ehci-hcd.  Simply carry out the same actions as the "dead:" statement
> label in ehci_irq() -- that is, do the same thing as if an interrupt
> occurred with the STS_FATAL bit set.  That code is all properly 
> synchronized.

Sometimes, there are no STS_FATAL and STA_ERR when ESD occurs.
So, you suggest do the same thing for STS_FATAL at my esd_recovery_process?

> 
> Then unbind the driver from the controller and rebind it.  Rebinding
> will reset the controller.
> 

You mean unbind the controller driver?  Any existed API can be called?
I can't do rmmod at that time.

Thanks.

-- 

Best Regards,
Peter Chen

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