Re: [linux-pm] swsusp regression [Was: 2.6.17-mm1]

[Greg KH <greg@kroah.com>]

On Thu, Jun 22, 2006 at 03:57:24PM -0400, Alan Stern wrote:
> On Thu, 22 Jun 2006, Greg KH wrote:
> 
> > > There are several possible ways to fix this.  One is to add suspend and 
> > > resume routines to the endpoint-device driver.  Another is to change the 
> > > code that checks for the children being suspended, to make it check only 
> > > for child USB devices and not child endpoints.
> > 
> > I think it needs to check for _USB_ devices, not just any old device
> > that could possibly be attached to the main USB device (as this one is.)
> > What's to stop any other struct device to bind here and cause the same
> > problem?
> 
> In my upcoming patches for USB core suspend improvements, one of the 
> changes affects this very piece of code.  Instead of looping over all 
> child devices in the driver-model sense, it loops over all interfaces in 
> the active configuration, which is all we care about right here.
> 
> > Ok, the problem is in verify_suspended(), we are not detecting what type
> > of device this is.
> > 
> > Alan, what are you trying to check for here?  What "bogus requests" were
> > you seeing from sysfs that you are trying to filter out?
> 
> I didn't write that routine, Dave Brownell did.  It has been there for
> ages.

Sorry for the misattribution, I should have checked closer.

> The "bogus requests" are attempts by the user to suspend a USB
> device (by writing to /sys/devices/.../power/state) without first
> suspending all its children and interfaces.
> 
> (This can't happen when doing a global suspend because the PM core 
> iterates through the entire device tree.  It matters only for "runtime" or 
> "selective" suspend.)

Then why is people hitting this now?  I guess no one had hooked a struct
device to a struct usb_device before, only interfaces.

> The two easiest ways to fix the problem are:
> 
> 	Change the code to look through the interfaces in the active
> 	configuration instead of using device_for_each_child;

Or at least verify that they are looking at an interface, just blindly
poking at a child device isn't very nice :(

> or
> 
> 	Revert your "endpoints are devices" patch until my upcoming
> 	changes are in place.

I'll work on a fix-up patch based on the first option :)

thanks,

greg k-h