* Why USB Link Power Management only for devices connected to root hub
@ 2012-05-22 6:12 prasannatsmkumar
2012-05-24 4:45 ` Greg KH
0 siblings, 1 reply; 2+ messages in thread
From: prasannatsmkumar @ 2012-05-22 6:12 UTC (permalink / raw)
To: linux-kernel
I have started looking into USB stuff. In the EHCI driver code I could
see the comment that "we only support lpm device connected to root hub
yet" in drivers/usb/host/ehci-pci.c line 466 (3.4 kernel -
http://lxr.free-electrons.com/source/drivers/usb/host/ehci-pci.c#L466).
Is there any reason to not support lpm in devices connected to hub
(other than root hub)? Also inside ehci_lpm_check function in
drivers/usb/host/ehci-lpm.c (3.4 kernel -
http://lxr.free-electrons.com/source/drivers/usb/host/ehci-lpm.c) the
USB device is asked to go to LPM mode and there is a wait for 10ms. I
guess the LPM transition (L0 to L1 state transition) should take place
within some micro seconds then why should we wait for 10ms for ACK?
Thanks,
Prasanna Kumar T S M
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Why USB Link Power Management only for devices connected to root hub
2012-05-22 6:12 Why USB Link Power Management only for devices connected to root hub prasannatsmkumar
@ 2012-05-24 4:45 ` Greg KH
0 siblings, 0 replies; 2+ messages in thread
From: Greg KH @ 2012-05-24 4:45 UTC (permalink / raw)
To: prasannatsmkumar; +Cc: linux-kernel
On Tue, May 22, 2012 at 11:42:28AM +0530, prasannatsmkumar wrote:
> I have started looking into USB stuff. In the EHCI driver code I could
> see the comment that "we only support lpm device connected to root hub
> yet" in drivers/usb/host/ehci-pci.c line 466 (3.4 kernel -
> http://lxr.free-electrons.com/source/drivers/usb/host/ehci-pci.c#L466).
> Is there any reason to not support lpm in devices connected to hub
> (other than root hub)? Also inside ehci_lpm_check function in
> drivers/usb/host/ehci-lpm.c (3.4 kernel -
> http://lxr.free-electrons.com/source/drivers/usb/host/ehci-lpm.c) the
> USB device is asked to go to LPM mode and there is a wait for 10ms. I
> guess the LPM transition (L0 to L1 state transition) should take place
> within some micro seconds then why should we wait for 10ms for ACK?
Please as USB-specific questions like this on the linux-usb mailing list
if you wish to get answers.
greg k-h
^ permalink raw reply [flat|nested] 2+ messages in thread
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2012-05-22 6:12 Why USB Link Power Management only for devices connected to root hub prasannatsmkumar
2012-05-24 4:45 ` Greg KH
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