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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