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

Uwe Kleine-König
2018-07-05T05:23:46Z

Hello,

On Wed, Jul 04, 2018 at 09:13:42PM +0200, Janusz Krzysztofik wrote:
> 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@gmail.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@gmail.com>
> > > ---
> > > If accepted, please add
> > >
> > > Suggested-by: Boris Brezillon <boris.brezillon@bootlin.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.

TL;DR: Either I don't understand the implication for
drivers/i2c/busses/i2c-imx.c or everything is fine.

Given that only i2c_imx_init_recovery_info() uses gpio functions I assume
you mean:

rinfo->sda_gpiod = devm_gpiod_get(&pdev->dev, "sda", GPIOD_IN);
rinfo->scl_gpiod = devm_gpiod_get(&pdev->dev, "scl", GPIOD_OUT_HIGH);

if (PTR_ERR(rinfo->sda_gpiod) == -EPROBE_DEFER ||
PTR_ERR(rinfo->scl_gpiod) == -EPROBE_DEFER) {
return -EPROBE_DEFER;
} else if (IS_ERR(rinfo->sda_gpiod) ||
IS_ERR(rinfo->scl_gpiod) ||
IS_ERR(i2c_imx->pinctrl_pins_default) ||
IS_ERR(i2c_imx->pinctrl_pins_gpio)) {
dev_dbg(&pdev->dev, "recovery information incomplete\n");
return 0;
}

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.

Best regards
Uwe

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