Re: [PATCH] gpiolib: Defer on non-DT find_chip_by_name() failure

Janusz Krzysztofik
2018-07-06T18:58:34Z

> >> 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