linux-kernel - Re: [PATCH v3 2/2] gnss: ubx: add support for the safeboot gpio

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Message-ID: <aR84-rVwQYFmhfOW@hovoldconsulting.com>
Date: Thu, 20 Nov 2025 16:51:22 +0100
From: Johan Hovold <johan@...nel.org>
To: alejandroe1@...tab.com
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: Re: [PATCH v3 2/2] gnss: ubx: add support for the safeboot gpio

On Fri, Nov 14, 2025 at 03:59:24PM +0100, Johan Hovold wrote:
> On Thu, Sep 11, 2025 at 02:58:29PM +0200, Alejandro Enrique via B4 Relay wrote:
> > From: Alejandro Enrique <alejandroe1@...tab.com>
> > 
> > U-Blox 8/M8/M9 chip have a pin to start it in safeboot mode, to be
> > used to recover from situations where the flash content has become
> > corrupted and needs to be restored. If this pin is asserted at power
> > up/reset, the receiver starts in safeboot mode and GNSS operation is
> > disabled.
> > 
> > Deassert the safeboot pin when probing this driver.

> Note however that both the RESET_N and SAFEBOOT_N pins should be
> declared as open-drain to avoid driving them while the main supply is
> off.
> 
> I added a comment about this to the commit message about this when
> applying and will send a follow-on patch to update the binding example.

I was playing with the idea of adding a warning about this to the driver
when realised that there would typically be a level shifter for these
signals that makes sure they are not driven while the supply is off so I
dropped the comment instead.

Johan