Re: [alsa-devel] [PATCH 5/6] mtd: rawnand: ams-delta: use GPIO lookup table

Ladislav Michl
2018-05-20T19:27:11Z

On Sat, May 19, 2018 at 11:55:51PM +0200, Janusz Krzysztofik wrote:
> 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;

Driver will just use worst case delay instead of RDY signal, so this
is perhaps too strict. I will work with degraded performance.

ladis

> }
>
> + 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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