linux-kernel - Re: [RFC PATCH 2/8] mtd: rawnand: ams-delta: Write protect device during probe

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Date:   Fri, 20 Jul 2018 20:02:02 +0200
From:   Janusz Krzysztofik <jmkrzyszt@...il.com>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Tony Lindgren <tony@...mide.com>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        linux-mtd@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
Subject: Re: [RFC PATCH 2/8] mtd: rawnand: ams-delta: Write protect device during probe

On Thursday, July 19, 2018 8:22:00 AM CEST Boris Brezillon wrote:
> On Thu, 19 Jul 2018 01:57:04 +0200
> Janusz Krzysztofik <jmkrzyszt@...il.com> wrote:
> 
> > Initialize NWP GPIO pin low to protect the device from hazard during
> > probe.  Release write protection as soon as the device is under
> > control.
> > 
> > Signed-off-by: Janusz Krzysztofik <jmkrzyszt@...il.com>
> > ---
> >  drivers/mtd/nand/raw/ams-delta.c | 10 ++++++++--
> >  1 file changed, 8 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/mtd/nand/raw/ams-delta.c b/drivers/mtd/nand/raw/ams-delta.c
> > index 48233d638d2a..6ac38e9cfa1a 100644
> > --- a/drivers/mtd/nand/raw/ams-delta.c
> > +++ b/drivers/mtd/nand/raw/ams-delta.c
> > @@ -219,8 +219,8 @@ static int ams_delta_init(struct platform_device *pdev)
> >  
> >  	platform_set_drvdata(pdev, priv);
> >  
> > -	/* Set chip enabled, but  */
> > -	priv->gpiod_nwp = devm_gpiod_get(&pdev->dev, "nwp", GPIOD_OUT_HIGH);
> > +	/* Set chip enabled but write protected */
> > +	priv->gpiod_nwp = devm_gpiod_get(&pdev->dev, "nwp", GPIOD_OUT_LOW);
> >  	if (IS_ERR(priv->gpiod_nwp)) {
> >  		err = PTR_ERR(priv->gpiod_nwp);
> >  		dev_err(&pdev->dev, "NWP GPIO request failed (%d)\n", err);
> > @@ -267,6 +267,9 @@ static int ams_delta_init(struct platform_device *pdev)
> >  	if (err)
> >  		goto out_mtd;
> >  
> > +	/* As soon as the device is found, release write protection */
> > +	gpiod_set_value(priv->gpiod_nwp, 1);
> 
> Please don't do that until we have a generic way to assert/deassert WP
> from the core. I agree that we shouldn't write things in the
> nand_scan() path, but I'd be more comfortable if the core had control
> on this pin just in case we ever need to disable write-protection
> during chip detection/initialization.

OK, I can drop this patch for now if that's what you suggest.
 
Thanks,
Janusz