linux-kernel - Re: [PATCH v3 5/7] gpio: Add GPIO Aggregator/Repeater driver

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Message-ID: <d44598a5-184e-078c-1d6c-a99b522f7e26@mentor.com>
Date:   Tue, 3 Dec 2019 14:21:21 +0530
From:   Harish Jenny K N <harish_kandiga@...tor.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Jonathan Corbet <corbet@....net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Eugeniu Rosca <erosca@...adit-jv.com>,
        Alexander Graf <graf@...zon.com>,
        Peter Maydell <peter.maydell@...aro.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Phil Reid <preid@...ctromag.com.au>,
        Marc Zyngier <marc.zyngier@....com>,
        Christoffer Dall <christoffer.dall@....com>,
        Magnus Damm <magnus.damm@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        QEMU Developers <qemu-devel@...gnu.org>
Subject: Re: [PATCH v3 5/7] gpio: Add GPIO Aggregator/Repeater driver


On 03/12/19 1:47 PM, Geert Uytterhoeven wrote:
> Hi Harish,
>
> On Tue, Dec 3, 2019 at 6:42 AM Harish Jenny K N
> <harish_kandiga@...tor.com> wrote:
>>> +static int gpio_aggregator_probe(struct platform_device *pdev)
>>> +{
>>> +     struct device *dev = &pdev->dev;
>>> +     struct gpio_desc **descs;
>>> +     struct gpiochip_fwd *fwd;
>>> +     int i, n;
>>> +
>>> +     n = gpiod_count(dev, NULL);
>>> +     if (n < 0)
>>> +             return n;
>>> +
>>> +     descs = devm_kmalloc_array(dev, n, sizeof(*descs), GFP_KERNEL);
>>> +     if (!descs)
>>> +             return -ENOMEM;
>>> +
>>> +     for (i = 0; i < n; i++) {
>>> +             descs[i] = devm_gpiod_get_index(dev, NULL, i, GPIOD_ASIS);
>> can you please add this check as well as we need to return EPROBE_DEFER.
>>
>> if (desc[i] == ERR_PTR(-ENOENT))
>> <                 return -EPROBE_DEFER;
> So gpiod_get_index() nevers return -EPROBE_DEFER, but returns -ENOENT
> instead?
> How can a driver distinguish between "GPIO not found" and "gpiochip driver
> not yet initialized"?
> Worse, so the *_optional() variants will return NULL in both cases, too, so
> the caller will always fall back to optional GPIO not present?
>
> Or am I missing something?
>
> Gr{oetje,eeting}s,
>
>                         Geert


We had earlier tested our changes on 4.14 kernel and the explicit return of -EPROBE_DEFER was needed in the inverter driver.

probably the commit 6662ae6af82df10259a70c7569b4c12ea7f3ba93 ( gpiolib: Keep returning EPROBE_DEFER when we should)

has fixed the issue and now it returns -EPROBE_DEFER.  you can ignore this comment as of now. I will test and let you know if needed.


Thanks,

Harish