From: Greg KH <gregkh@linuxfoundation.org>
To: prasannatsmkumar <prasannatsmkumar@gmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Why USB Link Power Management only for devices connected to root hub
Date: Wed, 23 May 2012 21:45:37 -0700 [thread overview]
Message-ID: <20120524044537.GB14325@kroah.com> (raw)
In-Reply-To: <CANc+2y50jirP=_V0qBkDuVwkhcmJWo3tQ-rwnxOtw3GQ5gP3tQ@mail.gmail.com>
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
prev parent reply other threads:[~2012-05-24 4:45 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-22 6:12 prasannatsmkumar
2012-05-24 4:45 ` Greg KH [this message]
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