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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Wed, 3 Feb 2021 09:15:48 +0100
Message-ID: <CAMuHMdWyA3y1PYff5X9DoPaj0TREK3jFe_P+e+rNVb1K-kRDbA@mail.gmail.com>
Subject: Re: [PATCH v2 0/3] Make fw_devlink=on more forgiving
To:     Saravana Kannan <saravanak@google.com>
Cc:     Martin Kaiser <martin@kaiser.cx>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Marc Zyngier <maz@kernel.org>,
        Tudor Ambarus <Tudor.Ambarus@microchip.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Len Brown <lenb@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        Android Kernel Team <kernel-team@android.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hi Saravana,

On Wed, Feb 3, 2021 at 9:11 AM Saravana Kannan <saravanak@google.com> wrote:
> On Tue, Feb 2, 2021 at 11:55 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Tue, Feb 2, 2021 at 11:44 PM Saravana Kannan <saravanak@google.com> wrote:
> > > On Tue, Feb 2, 2021 at 1:22 PM Martin Kaiser <martin@kaiser.cx> wrote:
> > > > Thus wrote Saravana Kannan (saravanak@google.com):
> > > > All of those drivers have a gpio in
> > > > their device-tree node, such as
> > > >
> > > > my_driver {
> > > >    gpio_test1 = <&gpio1 0 0>;
> > > >    ...
> > > > };
> > > >
> > > > with gpio1 from arch/arm/boot/dts/imx25.dtsi.
> > > >
> > > > The probe function calls
> > > >
> > > > of_get_named_gpio(np, "gpio_test1", 0);
> > > >
> > > > to get the gpio. This fails with -EINVAL.
> > >
> > > And you didn't see this issue with the fsl,avic patch?
> > >
> > > The property you are using is not a standard GPIO binding (-gpios,
> > > gpio, gpios) and I'm not surprised it's not working. The gpio1 is
> > > probably getting probe deferred and ends up running after "my_driver".
> >
> > So my_driver doesn't support deferred probe, as of_get_named_gpio()
> > returns -EINVAL instead of -EPROBE_DEFER?
> > Converting my_driver from of_get_named_gpio() to the gpiod_*() API
> > should at least make the driver support probe deferral, after which I
> > expect it to start working again on reprobe?
>
> The way I understood the API/example, you can't just change the code
> and have it work. The DT itself isn't using standard bindings. And we

Oh, right.

> can't make kernel changes that assume the DT has been changed to match
> the code. So, the best we could do is have of_get_named_gpio() return
> -EPROBE_DEFER if it doesn't find the GPIO -- assuming that doesn't
> break other users. Or have this specific driver remap the -EINVAL to
> -EPROBE_DEFER.

The latter would hide real errors, too, and would cause futile reprobes.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds