linux-kernel - Re: [PATCH v3 1/2] usb: host: ehci-tegra: Grab the correct UTMI pads reset

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Message-ID: <20160504203037.GC21480@mithrandir.ba.sec>
Date:	Wed, 4 May 2016 22:30:45 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Jon Hunter <jonathanh@...dia.com>, linux-usb@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] usb: host: ehci-tegra: Grab the correct UTMI pads
 reset

On Wed, May 04, 2016 at 11:14:50AM -0600, Stephen Warren wrote:
> On 05/04/2016 08:39 AM, Thierry Reding wrote:
> > From: Thierry Reding <treding@...dia.com>
> > 
> > There are three EHCI controllers on Tegra SoCs, each with its own reset
> > line. However, the first controller contains a set of UTMI configuration
> > registers that are shared with its siblings. These registers will only
> > be reset as part of the first controller's reset. For proper operation
> > it must be ensured that the UTMI configuration registers are reset
> > before any of the EHCI controllers are enabled, irrespective of the
> > probe order.
> > 
> > Commit a47cc24cd1e5 ("USB: EHCI: tegra: Fix probe order issue leading to
> > broken USB") introduced code that ensures the first controller is always
> > reset before setting up any of the controllers, and is never again reset
> > afterwards.
> > 
> > This code, however, grabs the wrong reset. Each EHCI controller has two
> > reset controls attached: 1) the USB controller reset and 2) the UTMI
> > pads reset (really the first controller's reset). In order to reset the
> > UTMI pads registers the code must grab the second reset, but instead it
> > grabbing the first.
> > 
> > Signed-off-by: Thierry Reding <treding@...dia.com>
> > ---
> > Stephen, Alex, Jon, have you ever encountered cases where UTMI might not
> > have worked correctly? It seems that this code was pulsing the wrong
> > reset line and therefore the UTMI pads would never be reset unless the
> > first USB controller was probed before all others. I've never seen any
> > such problems myself, so I'm unsure about whether it's worth Cc'ing the
> > patch to stable@...r.kernel.org.
> 
> I don't think I recall seeing USB issues like that, although I don't use USB
> a huge amount. Perhaps the issue just never happens because we always have
> USB1 enabled, and it's physically present in the DTB first, so it always
> happens to get probed first?

Actually for Jetson TK1 we don't enable USB1. It's interesting because
v1 of patch 2/2 only fixed the issue for device where USB1 was indeed
enabled and probed first (I tested on TrimSlice). Running these fixes
through EIMT I noticed that it didn't fix it in the general case and I
was still seeing the warning on Jetson TK1 for example.

That's in fact what tipped me off about the consumer name, because I was
seeing reset 58 (USB2) being requested twice.

Thierry

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