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

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Message-ID: <CAHp75Ved2nw1JKnXT2Jxnw4XLsby1eVJU6cfBjE2sp4LP4Kwmg@mail.gmail.com>
Date:   Sun, 20 May 2018 17:44:31 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Janusz Krzysztofik <jmkrzyszt@...il.com>
Cc:     Tony Lindgren <tony@...mide.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Mark Brown <broonie@...nel.org>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        Richard Weinberger <richard@....at>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Jarkko Nikula <jarkko.nikula@...mer.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-input <linux-input@...r.kernel.org>,
        "open list:MEMORY TECHNOLOGY..." <linux-mtd@...ts.infradead.org>,
        linux-fbdev@...r.kernel.org,
        ALSA Development Mailing List <alsa-devel@...a-project.org>
Subject: Re: [PATCH 5/6] mtd: rawnand: ams-delta: use GPIO lookup table

On Sun, May 20, 2018 at 12:55 AM, Janusz Krzysztofik
<jmkrzyszt@...il.com> 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@...il.com>
> wrote:

>> 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;

This makes sense.

Though, I completely dislike "rdy" name of GPIO. Where is it documented?

>> >> > +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.

Yes, but the code you provided in patch looks somehow suspicious. OK,
I let Linus decide whtat to do with that.

-- 
With Best Regards,
Andy Shevchenko