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

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Message-ID: <572A2E0A.8040408@wwwdotorg.org>
Date:	Wed, 4 May 2016 11:14:50 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Thierry Reding <thierry.reding@...il.com>
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 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?