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

From: Stephen Warren
Date: Wed May 04 2016 - 13:14:58 EST

On 05/04/2016 08:39 AM, Thierry Reding wrote:
From: Thierry Reding <treding@xxxxxxxxxx>

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

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@xxxxxxxxxx>
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@xxxxxxxxxxxxxxxx

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?