linux-kernel - Re: [PATCH] usb: xhci-plat: Enable USB 2.0 hardware LPM support for platform xHCs

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Date:	Wed, 21 Aug 2013 17:45:14 -0700
From:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
To:	Julius Werner <jwerner@...omium.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Vincent Palatin <vpalatin@...omium.org>,
	Benson Leung <bleung@...omium.org>,
	Felipe Balbi <balbi@...com>, mathias.nyman@...ux.intel.com
Subject: Re: [PATCH] usb: xhci-plat: Enable USB 2.0 hardware LPM support for
 platform xHCs

On Wed, Aug 21, 2013 at 02:43:55PM -0700, Julius Werner wrote:
> > Thanks for the patch!  Did you test with a USB analyzer to see if the
> > device was actually going into USB 2.0 Link PM?  I'd like to confirm we
> > really aren't breaking anything for DW3 hosts by enabling this.
> 
> Yes, I did. The LPM transfers on the analyzer look good and the device
> works as expected.

Ok, good to know.  Greg, is your USB tree still open for feature
requests?  I wouldn't normally send you usb-next requests so late, but
this is pretty simple patch to extend a feature that's already in your
usb-next tree.

> My platform only runs a 3.8 derivative, though, so I now have also
> cherry-picked the BESL patches that went in since then to make sure
> they don't break things. I had problems on one device until I found
> the XHCI_BLC fix Mathias sent out this morning, so you should pick
> that one up first. (Without it LPM doesn't break completely but seems
> to assert resume for less time than the HIRD defines, so the device
> sometimes gets confused and resets. I can't figure out how BESL is
> really supposed to work since the XHCI spec from 8/14/12 where it's
> supposedly defined doesn't seem to be publicly available.)

You need the USB 2.0 spec errata from 2011-11 that describes the changes
made for BESL as well.  It's in the USB2-LPM-Errata-final.pdf and
USB2_LinkPowerMangement_ECN[final].pdf files in this zip file:

http://www.usb.org/developers/docs/usb_20_070113.zip

I agree though, it's all a confusing mess for documentation on USB 2.0
Link PM.

Sarah Sharp
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