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SubjectRe: [PATCH 5/6] mtd: rawnand: ams-delta: use GPIO lookup table
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On Saturday, May 19, 2018 8:00:38 PM CEST Andy Shevchenko wrote:
> On Sat, May 19, 2018 at 2:15 AM, Janusz Krzysztofik <jmkrzyszt@gmail.com>
wrote:
> > On Friday, May 18, 2018 11:21:14 PM CEST Andy Shevchenko wrote:
> >> On Sat, May 19, 2018 at 12:09 AM, Janusz Krzysztofik
> >>
> >> <jmkrzyszt@gmail.com> wrote:
> >> > + gpiod_rdy = devm_gpiod_get_optional(&pdev->dev, "rdy",
> >> > GPIOD_IN);
> >> > + if (!IS_ERR_OR_NULL(gpiod_rdy)) {
> >>
> >> So, is it optional or not at the end?
> >> If it is, why do we check for NULL?
> >
> > As far as I can understand, nand_chip->dev_ready() callback is optional.
> > That's why I decided to use the _optional variant of devm_gpiod_get(). In
> > case of ams-delta, the dev_ready() callback depends on availability of
> > the 'rdy' GPIO pin. As a consequence, I'm checking for both NULL and ERR
> > in order to decide if dev_ready() will be supported.
> >
> > I can pretty well replace it with the standard form and check for ERR only
> > if the purpose of the _optional form is different.
>
> NULL check in practice discards the _optional part of gpiod_get(). So,
> either you use non-optional variant and decide how to handle an
> errors, or user _optional w/o NULL check.

OK, I'm going to use something like the below while submitting v2:

- gpiod_rdy = devm_gpiod_get_optional(&pdev->dev, "rdy", GPIOD_IN);
- if (!IS_ERR_OR_NULL(gpiod_rdy)) {
- this->dev_ready = ams_delta_nand_ready;
- } else {
- this->dev_ready = NULL;
- pr_notice("Couldn't request gpio for Delta NAND ready.\n");
+ priv->gpiod_rdy = devm_gpiod_get_optional(&pdev->dev, "rdy",
+ GPIOD_IN);
+ if (IS_ERR(priv->gpiod_rdy)) {
+ err = PTR_ERR(priv->gpiod_nwp);
+ dev_warn(&pdev->dev, "RDY GPIO request failed (%d)\n", err);
+ goto err_gpiod;
}

+ if (priv->gpiod_rdy)
+ this->dev_ready = ams_delta_nand_ready;

>
> >> > +err_gpiod:
> >> > + if (err == -ENODEV || err == -ENOENT)
> >> > + err = -EPROBE_DEFER;
> >>
> >> Hmm...
> >
> > Amstrad Delta uses gpio-mmio driver. Unfortunatelty that driver is not
> > availble before device init phase, unlike other crucial GPIO drivers which
> > are initialized earlier, e.g. during the postcore or at latetst the
> > subsys phase. Hence, devices which depend on GPIO pins provided by
> > gpio-mmio must either be declared late or fail softly so they get another
> > chance of being probed succesfully.
> >
> > I thought of replacing the gpio-mmio platform driver with bgpio functions
> > it exports but for now I haven't implemented it, not even shared the
> > idea.
> >
> > Does it really hurt to return -EPROBE_DEFER if a GPIO pin can't be
> > obtained?
> I'm only concerned if it would be an infinite defer in the case when
> driver will never appear.
> But I don't remember the details.

Deferred probes are handled effectively during late_initcall, no risk of
infinite defer, see drivers/base/dd.c for details.

Thanks,
Janusz



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