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

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Message-ID: <CAN=L63pq6WzietQQpdfJ9K3sH2EaQsgRY4RauJsgqV7F2S8U_w@mail.gmail.com>
Date: Mon, 17 Nov 2025 17:33:49 +0100
From: Alejandro Enrique <alejandroe1@...tab.com>
To: Johan Hovold <johan@...nel.org>
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 3:59 PM Johan Hovold <johan@...nel.org> 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.
> >
> > Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> > Signed-off-by: Alejandro Enrique <alejandroe1@...tab.com>
>
> Sorry about the late feedback on this. I had to think about how best to
> handle this, given that we don't have an interface yet to actually
> assert these pins.
>
> I guess we can go ahead and request them at probe as you're doing here
> and add an interface for controlling them later if needed (instead of
> not claiming them and allowing emergency control through gpiolib).
>
> > @@ -82,6 +83,13 @@ static int ubx_probe(struct serdev_device *serdev)
> >
> >       data = gnss_serial_get_drvdata(gserial);
> >
> > +     /* Deassert safeboot */
> > +     safeboot = devm_gpiod_get_optional(&serdev->dev, "safeboot", GPIOD_OUT_LOW);
> > +     if (IS_ERR(safeboot)) {
> > +             ret = PTR_ERR(safeboot);
> > +             goto err_free_gserial;
> > +     }
> > +
> >       data->vcc = devm_regulator_get(&serdev->dev, "vcc");
>
> Note that the driver is not enabling the supply until open() so I moved
> the deassert to after the supplies have been requested (but before reset
> is deasserted).
>
> 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 will keep that in mind.
Thank you for the note and your time in reviewing this.
>
>
> 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.
>
> >       if (IS_ERR(data->vcc)) {
> >               ret = PTR_ERR(data->vcc);
>
> Johan