linux-kernel - Re: [PATCH] gpiolib: Defer on non-DT find_chip_by

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Date:   Wed, 04 Jul 2018 21:13:42 +0200
From:   Janusz Krzysztofik <jmkrzyszt@...il.com>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lee Jones <lee.jones@...aro.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        Phil Reid <preid@...ctromag.com.au>,
        Lucas Stach <l.stach@...gutronix.de>,
        Clemens Gruber <clemens.gruber@...ruber.com>,
        Peter Rosin <peda@...ntia.se>, patches@...nsource.cirrus.com,
        linux-i2c@...r.kernel.org, Janusz Krzysztofik <jmkrzyszt@...il.com>
Subject: Re: [PATCH] gpiolib: Defer on non-DT find_chip_by_name() failure

On Tuesday, July 3, 2018 7:31:41 PM CEST Boris Brezillon wrote:
> Hi Janusz,
> 
> On Tue,  3 Jul 2018 19:26:35 +0200
> 
> Janusz Krzysztofik <jmkrzyszt@...il.com> wrote:
> > Avoid replication of error code conversion in non-DT GPIO consumers'
> > code by returning -EPROBE_DEFER from gpiod_find() in case a chip
> > identified by its label in a registered lookup table is not ready.
> > 
> > See https://lkml.org/lkml/2018/5/30/176 for example case.
> > 
> > Signed-off-by: Janusz Krzysztofik <jmkrzyszt@...il.com>
> > ---
> > If accepted, please add
> > 
> > 	Suggested-by: Boris Brezillon <boris.brezillon@...tlin.com>
> > 
> > if Boris doesn't mind.
> > 
> > Thanks,
> > Janusz
> > 
> >  drivers/gpio/gpiolib.c | 13 ++++++++++---
> >  1 file changed, 10 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > index e11a3bb03820..15dc77c80328 100644
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -3639,9 +3639,16 @@ static struct gpio_desc *gpiod_find(struct device
> > *dev, const char *con_id,> 
> >  		chip = find_chip_by_name(p->chip_label);
> >  		
> >  		if (!chip) {
> > 
> > -			dev_err(dev, "cannot find GPIO chip %s\n",
> > -				p->chip_label);
> > -			return ERR_PTR(-ENODEV);
> > +			/*
> > +			 * As the lookup table indicates a chip with
> > +			 * p->chip_label should exist, assume it may
> > +			 * still appear latar and let the interested
> 
> 					^ later
> 
> > +			 * consumer be probed again or let the Deferred
> > +			 * Probe infrastructure handle the error.
> > +			 */
> > +			dev_warn(dev, "cannot find GPIO chip %s, deferring\n",
> > +				 p->chip_label);
> > +			return ERR_PTR(-EPROBE_DEFER);
> > 
> >  		}
> >  		
> >  		if (chip->ngpio <= p->chip_hwnum) {
> 
> Looks good otherwise. Let's hope we're not breaking implementations
> testing for -ENODEV...

I've reviewed them all and found two which I think may be affected:
- drivers/mfd/arizona-core.c,
- drivers/i2c/busses/i2c-imx.c.
As far as I can understand the code, both depend on error != -EPROBE_DEFER in 
order to continue in degraded mode. I'm adding their maintainers to the loop.

Thanks,
Janusz