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List:       linux-usb-users
Subject:    [Linux-usb-users] RE: [linux-usb-devel] Re: Linux MIPS - bus_to_virt()/virt_to_bus(
From:       "Dunlap, Randy" <randy.dunlap () intel ! com>
Date:       2000-09-29 17:13:58
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> > I also notice a lot of bus_to_virt()/virt_to_bus() 
> conversions.  What is
> > the purpose of getting bus address?
> > 
> 
> I am still curious about this.  

Have you read linux/Documentation/IO-mapping.txt ?
And maybe look at
http://gtf.org/garzik/drivers/LinuxExpo2000_Paris/expo2000paris.htm,
which is Jeff Garzik's presentation on
"Writing Portable Device Drivers".


> > Unlike i386, MIPS cache does not snoop on memory bus, and 
> therefore it
> > does not maitain cache consistency automatically.  I am afraid if a
> > device gets the bus address and modifies the system RAM content, the
> > driver would still read stale data through the cached 
> virtual addresses.
> > 
> > Is this a possible source of problem?
> > 
> 
> I just verified that cache consistency may not be the 
> problem.  I turned
> off the cache while I ran Linux.  I still get the same error.
> 
> ---------
> 
> usb.c: USB new device connect, assigned device number 2
> usb_control/bulk_msg: timeout
> usb-ohci.c: unlink URB timeout!
> usb.c: USB device not accepting new address (error=-145)
> usb.c: USB new device connect, assigned device number -1
> usb.c: USB device not accepting new address (error=-12)
> usb.c: USB disconnect on device -1
> 
> ----------
> 
> Now I run out of ideas.  Apparently the timeout happens inside
> usb_start_wait_urb().  After the code calls schedule_timeout(), who is
> supposed to wake it up before the timeout happens?  An interrupt from
> USB controller?

Yes, normal flow is for a USB host controller interrupt to
keep the timeout from happening.

~Randy

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