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    SubjectRe: [PATCH v3 1/2] usb: host: ehci-tegra: Grab the correct UTMI pads reset
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    On 05/04/2016 08:39 AM, Thierry Reding wrote:
    > From: Thierry Reding <treding@nvidia.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@nvidia.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@vger.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?

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