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

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Message-ID: <A2CA0424C0A6F04399FB9E1CD98E030458DEEC7E@US01WEMBX2.internal.synopsys.com>
Date:	Thu, 29 Aug 2013 18:40:44 +0000
From:	Paul Zimmerman <Paul.Zimmerman@...opsys.com>
To:	Julius Werner <jwerner@...omium.org>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
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" <mathias.nyman@...ux.intel.com>,
	Josh Triplett <josh.triplett@...el.com>
Subject: RE: [PATCH] usb: xhci-plat: Enable USB 2.0 hardware LPM support for
 platform xHCs

> From: jwerner@...gle.com [mailto:jwerner@...gle.com] On Behalf Of Julius Werner
> Sent: Thursday, August 29, 2013 11:07 AM
> 
> > If you take a look at Table
> > 13: BESL/HIRD Encoding from the xHCI spec version including errata to
> > 08/14/2012
> 
> Could you please provide a link to that errata? I still cannot find
> it... but from your explanation, that design decision sounds pretty
> horrible. Why didn't they just choose not to set old HLC flag in BESL
> controllers? Seems like the only purpose it provides there is to make
> old drivers break.
> 
> Anyway, looks like we are stuck with it now, and need to deal with
> those mislabeled DWC3 versions. I agree with you that we should
> blacklist instead of whitelist, but I don't think the device tree is
> the best place to put that... we would have to figure out the exact
> DWC3 version for every processor/SoC dtsi file to determine if they
> are affected, and remember to keep that up to date as we added more.
> 
> I would instead propose to check for the revision register directly in
> the DWC3 stack. I think I could add a little check to dwc3_host_init()
> and hack the quirk bit into the newly created XHCI controller instance
> if required. However, I only have an old (unaffected) 1.85 controller
> for testing, so I would need Synopsys to provide me with the exact
> revision numbers affected (as read from the register) and to test the
> change for us.

OK, I did a little more digging, and it turns out the 2.41a version
_does_ set bit 20 in the protocol defined field if BESL support is
enabled. It wasn't mentioned in the "registers" section of the databook,
but there is a note to that effect in a different section.

So it looks like we don't need to worry about this for the DWC3
controllers, anyway. Sorry for the noise.

-- 
Paul

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