linux-kernel - Re: [PATCH v8 07/14] gpio: thunderx: Use the default parent apis for {request,release}

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Date:   Wed, 11 Mar 2020 09:09:43 -0700
From:   Tim Harvey <tharvey@...eworks.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Lokesh Vutla <lokeshvutla@...com>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, Nishanth Menon <nm@...com>,
        Jason Cooper <jason@...edaemon.net>,
        Linux ARM Mailing List <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        Tero Kristo <t-kristo@...com>, Sekhar Nori <nsekhar@...com>,
        Tony Lindgren <tony@...mide.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Device Tree Mailing List <devicetree@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH v8 07/14] gpio: thunderx: Use the default parent apis for {request,release}_resources

On Wed, Mar 11, 2020 at 8:43 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> Tim,
>
> Tim Harvey <tharvey@...eworks.com> writes:
> > On Tue, Apr 30, 2019 at 3:14 AM Lokesh Vutla <lokeshvutla@...com> wrote:
> >> -       if (parent_data && parent_data->chip->irq_request_resources) {
> >> -               r = parent_data->chip->irq_request_resources(parent_data);
> >> -               if (r)
> >> -                       goto error;
> >> -       }
> >> +       r = irq_chip_request_resources_parent(data);
> >> +       if (r)
> >> +               gpiochip_unlock_as_irq(&txgpio->chip, txline->line);
> >
> > This patch breaks irq resources for thunderx-gpio as
> > parent_data->chip->irq_request_resources is undefined thus your new
> > irq_chip_request_resources_parent() returns -ENOSYS causing this
> > function to return an error where as before it would happily return 0.
> >
> > Is the following the correct fix or should we qualify
> > data->parent_data->chip->irq_request_resources before calling
> > irq_chip_request_resources_parent() in thunderx-gpio?
>
> You are not supposed to fiddle with parent data at all. Just because C
> allows you is no excuse to violate abstractions in the first place.
>
> irq_chip_request_resources_parent() rightfully returns -ENOSYS when it
> can't request a resource from the parent chip because that chip does not
> have anything to offer.
>
> It's up to the caller to do something sensible with the return code. If
> your chip is happy with the parent not providing it then handle
> -ENOSYS. None of the chip callbacks should return -ENOSYS. If one does
> then that wants to be fixed.
>

Ok, makes sense. Thank you and Lokesh for the feedback. I just
submitted a patch to fix the thunderx-gpio breakage.

Best Regards,

Tim