Problem in HCD resume

Problem in HCD resume

[rasmit.ranjan]

Hi,
	I was trying suspend/resume of OHCI based host controller. I
suspend the device interface, device/port and the roothub interface/bus
selectively through sysfs.
According to Power Management sub-system if I resume the roothub
interface the all the downsteam devices( device/port and device
interface) should be resumed. That means power state file of
roothub,port/device,device interface should be 0. But power state of the
port/device remains 3. 
	I tried finding out the reasons. I went through the kernel code.
What I found out is, resuming any node is initiated through
usb_generic_device API. In that API first we change the
dev->power.power_state.event = PM_EVENT_ON which is the notification to
PM sub-system that now the device is not in suspended state, it is on
now and the power state file of the node is changed to 0. When I traced
the path for my case i.e. resuming the bus.
Here it goes:

Usb_generic_resume-->hub_resume-->hcd_bus_resume-->ohci_bus_resume-->fin
ish_device_resume.

Actually finish_device_resume is called from hub_resume and the
parameter passed to finish_device_resume is the usb_device structure
representing the device connected. Then for all the interfaces of the
device finish_device_resume calls usb_generic_resume.
So it is clear that expect the device all other node`s resume is
initiated from usb_generic_resume and this is the only API which does
dev->power.power_state.event = PM_EVENT_ON. As for device resume this is
not done, its power state remains 3 although the device is actually
resumed. 

Is my understanding correct? If yes then is it a known issue ? I am
using kernel 2.6.15.4.
So is ther any patch available for this?

Please suggest.

Thanks,
Rasmit.
    


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Re: Problem in HCD resume

[Alan Stern]

On Fri, 2 Jun 2006 rasmit.ranjan@wipro.com wrote:

> Hi,
> 	I was trying suspend/resume of OHCI based host controller. I
> suspend the device interface, device/port and the roothub interface/bus
> selectively through sysfs.
> According to Power Management sub-system if I resume the roothub
> interface the all the downsteam devices( device/port and device
> interface) should be resumed.

This isn't true at all.  Selective resume of a device through sysfs is
_not_ expected to change the power state of the device's children.  The
fact that it does for USB devices is an historical artifact.  This
behavior will change in the near future.

>  That means power state file of
> roothub,port/device,device interface should be 0. But power state of the
> port/device remains 3. 
> 	I tried finding out the reasons. I went through the kernel code.
> What I found out is, resuming any node is initiated through
> usb_generic_device API. In that API first we change the
> dev->power.power_state.event = PM_EVENT_ON which is the notification to
> PM sub-system that now the device is not in suspended state, it is on
> now and the power state file of the node is changed to 0. When I traced
> the path for my case i.e. resuming the bus.
> Here it goes:
> 
> Usb_generic_resume-->hub_resume-->hcd_bus_resume-->ohci_bus_resume-->fin
> ish_device_resume.
> 
> Actually finish_device_resume is called from hub_resume and the
> parameter passed to finish_device_resume is the usb_device structure
> representing the device connected. Then for all the interfaces of the
> device finish_device_resume calls usb_generic_resume.
> So it is clear that expect the device all other node`s resume is
> initiated from usb_generic_resume and this is the only API which does
> dev->power.power_state.event = PM_EVENT_ON. As for device resume this is
> not done, its power state remains 3 although the device is actually
> resumed. 
> 
> Is my understanding correct?

It's hard to say, since you mentioned some things that don't matter and 
left out the big part that _does_ matter: The code in hub_resume that 
resumes child devices doesn't call usb_generic_resume.

>  If yes then is it a known issue ? I am
> using kernel 2.6.15.4.
> So is ther any patch available for this?

No.  You can write one if you want.  Since there will soon be a patch that
prevents the hub driver from waking up child devices, your problem
probably doesn't matter.

Alan Stern



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Re: Problem in HCD resume

[Pavel Machek]

On Fri 02-06-06 17:38:24, rasmit.ranjan@wipro.com wrote:
> Hi,
> 	I was trying suspend/resume of OHCI based host controller. I
> suspend the device interface, device/port and the roothub interface/bus
> selectively through sysfs.

sysfs suspend/resume interface is broken and only useful for
debugging. You'll need to invent new one.
							Pavel
-- 
Thanks for all the (sleeping) penguins.