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

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Date:   Fri, 06 Jul 2018 20:58:34 +0200
From:   Janusz Krzysztofik <jmkrzyszt@...il.com>
To:     Richard Fitzgerald <rf@...nsource.cirrus.com>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.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
Subject: Re: [PATCH] gpiolib: Defer on non-DT find_chip_by_name() failure

> >> On Wed, 04 Jul 2018, Janusz Krzysztofik wrote:
> >>> On Tuesday, July 3, 2018 7:31:41 PM CEST Boris Brezillon wrote:
> >>>> On Tue,  3 Jul 2018 19:26:35 +0200 Janusz Krzysztofik wrote:
> >>>>>   		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
> >>>>> +			 * 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);
> >>>>>   		}
> >>>> 
> >>>> 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.

On Thursday, July 5, 2018 7:23:46 AM CEST Uwe Kleine-König wrote:
> TL;DR: Either I don't understand the implication for
> drivers/i2c/busses/i2c-imx.c or everything is fine.
> ...
> So if a patch changes devm_gpiod_get() to return -EPROBE_DEFER in more
> cases that doesn't seem to hurt. Moreover TTBOMK this driver should only
> be used by dt-machines today such that changing gpio* for non-DT users
> shouldn't affect it.

On Friday, July 6, 2018 11:03:53 AM CEST Richard Fitzgerald wrote:
> The intention is that if the DT node is missing, the Arizona driver can run
> using only soft reset, though there are limitations in that mode.
> This should return -ENOENT so that the Arizona driver will continue without
> a GPIO.
> 
> If the DT defines a GPIO it is effectively saying that this GPIO is required
> so it is valid for the Arizona driver never to come up if the GPIO it is
> defined to depend on doesn't come up.

Uwe, Richard, thanks for clarifications.

I think we can assume the change is safe for all current implementations.

Thanks,
Janusz