linux-kernel - Re: [RFC PATCH] gpiolib: Move setting the flow handler and don't set it at all if there is a parent domain

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Date:   Mon, 4 Oct 2021 00:16:08 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Daniel Palmer <daniel@...f.com>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Marc Zyngier <maz@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] gpiolib: Move setting the flow handler and don't set
 it at all if there is a parent domain

Hi Daniel,

thanks for your patch!

On Sat, Oct 2, 2021 at 6:20 PM Daniel Palmer <daniel@...f.com> wrote:

> Calling irq_domain_set_info() before irq_domain_alloc_irqs_parent()
> can cause a null pointer dereference as the parent domain isn't
> ready yet.
>
> Move irq_domain_set_info() to after irq_domain_alloc_irqs_parent().
> A side effect of this is that irq_domain_set_info() will now overwrite
> the flow handler from the parent domain. So if there is a parent
> domain do not set the flow handler anymore.
>
> This allows gpio-msc313.c to level it's irq domain on top of the
> new irq controller in later SigmaStar SoCs without crashing.
>
> Link: https://lore.kernel.org/linux-arm-kernel/20210914100415.1549208-1-daniel@0x0f.com/
> Signed-off-by: Daniel Palmer <daniel@...f.com>
> Suggested-by: Marc Zyngier <maz@...nel.org>

If Marc says this is the way to go I think it is the way to go!

>         kfree(parent_arg);
> +
> +       if (!ret) {

Please just exit on error so invert this.

if (ret)
  return ret;

and just de-indent the below code (easier to follow)

> +               /* If there is a parent domain leave the flow handler alone */
> +               if (d->parent)
> +                       irq_domain_set_hwirq_and_chip(d,
> +                                                     irq,
> +                                                     hwirq,
> +                                                     gc->irq.chip,
> +                                                     gc);
> +               /* Otherwise set the flow handler supplied by the gpio driver */
> +               else
> +                       irq_domain_set_info(d,
> +                                           irq,
> +                                           hwirq,
> +                                           gc->irq.chip,
> +                                           gc,
> +                                           girq->handler,
> +                                           NULL, NULL);
> +               irq_set_probe(irq);
> +       }

Should we print an error if girq->handler is not NULL and we find
a parent domain, like
if (d->parent && girq->handler)
  dev_err(dev, "parent domain and flow handler both specified\n");

Yours,
Linus Walleij