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Date:   Thu, 23 Feb 2017 15:45:55 +0100
From:   Linus Walleij <>
To:     Rick Altherr <>
Cc:     "" <>,
        OpenBMC Maillist <>,
        Joel Stanley <>, Andrew Jeffery <>
Subject: Re: [PATCH linux] aspeed: pinctrl: Allow disabling Port D and Port E
 loopback mode

On Wed, Feb 15, 2017 at 7:09 AM, Rick Altherr <> wrote:

> Port D and port E GPIO loopback modes are commonly enabled via hardware
> straps for use with front-panel buttons.  When the BMC is powered
> off or fails to boot, the front-panel buttons are directly connected to
> the host chipset via the loopback to allow direct power-on and reset
> control. Once the BMC has booted, the loopback mode must be disabled for
> the BMC to take over control of host power-on and reset.
> Disabling these loopback modes requires writing to the hardware strap
> register which violates the current design of assuming the system
> designer chose the strap settings for a specific reason and they should
> be treated as read-only. Only the two bits of the strap register related
> to these loopback modes are allowed to be written and comments have been
> added to explain why.
> Signed-off-by: Rick Altherr <>

Patch applied with the ACKs for v4.12.

Linus Walleij

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