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Re: How to perform runtime pm for usb hcds?

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On Wed, 21 Nov 2007, jidong xiao wrote:

> > localhost:~ # echo 3 >/sys/devices/pci0000:00/0000:00:1d.0/power/state
> > -bash: echo: write error: Invalid argument
> >
> > But this command failed to work.(both usbcore and uhci-hcd are inserted already)
> > The kernel I am using is 2.6.22.1.
> >
> > Regards
> > Jason
> >
> 
> I also tried echo -n 3 > ...
> 
> echo -n 3 >/sys/devices/pci0000:00/0000:00:1d.0/usb1/1-0:1.0/power/state
> echo -n 3 >/sys/devices/pci0000:00/0000:00:1d.0/usb1/power/state
> echo -n 3 >/sys/devices/pci0000:00/0000:00:1d.0/power/state
> 
> The first two commands works well,but the third one doesn't.

Yes.  The PM core was changed (I don't remember exactly when) so that 
writes to power/state wouldn't always be accepted for all devices.  You 
can undo that change by commenting out the "if" and "return" statements 
at the start of drivers/base/power/sysfs.c:state_store().  But it's 
easier just to use the PCI-suspend patch I posted before.

> Then I do:
> 
> localhost:~ # lspci -vvv -s 1d.0
> 00:1d.0 USB Controller: Intel Corporation 82801FB/FBM/FR/FW/FRW (ICH6
> Family) USB UHCI #1 (rev 03) (prog-if 00 [UHCI])
>         Subsystem: Dell Unknown device 018f
>         Control: I/O+ Mem- BusMaster+ SpecCycle- MemWINV- VGASnoop-
> ParErr- Stepping- SERR- FastB2B-
>         Status: Cap- 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium
> >TAbort- <TAbort- <MAbort- >SERR- <PERR-
>         Latency: 0
>         Interrupt: pin A routed to IRQ 16
>         Region 4: I/O ports at bf80 [size=32]
> 
> Is "Cap-" indicating that the controller is not able to perform power
> management?

That's right.  Most UHCI controllers can't do it, although some of the 
controllers made by VIA can.

Alan Stern


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