linux-kernel - Re: [PATCH v3 3/5] gpio: gpiolib: Allow free() callback to be overridden

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Date:   Thu, 12 May 2022 13:48:53 +0100
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linus Walleij <linus.walleij@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Phil Edworthy <phil.edworthy@...esas.com>,
        Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [PATCH v3 3/5] gpio: gpiolib: Allow free() callback to be overridden

Hi Marc,

Thank you for the review.

On Thu, May 12, 2022 at 12:19 PM Marc Zyngier <maz@...nel.org> wrote:
>
> On Wed, 11 May 2022 19:32:08 +0100,
> Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com> wrote:
> >
> > Allow free() callback to be overridden from irq_domain_ops for
> > hierarchical chips.
> >
> > This allows drivers to free any resources which are allocated during
> > populate_parent_alloc_arg().
>
> Do you mean more than the fwspec? I don't see this being used.
>
The free callback is used in patch 5/5 where free is overridden by
rzg2l_gpio_irq_domain_free. I just gave an example there as an
populate_parent_alloc_arg()  In actual in the child_to_parent_hwirq
callback I am using a bitmap [0] to get a free tint slot, this bitmap
needs freeing up when the GPIO interrupt is released from the driver
that as when overridden free callback frees the allocated tint slot so
that its available for re-use.

> There is also the question of why we need to have dynamic allocation
> for the fwspec itself. Why isn't that a simple stack allocation in the
> context of gpiochip_hierarchy_irq_domain_alloc()?
>
you mean gpio core itself should handle the fwspec allocation/freeing?

[0] https://patchwork.kernel.org/project/linux-renesas-soc/patch/20220511183210.5248-6-prabhakar.mahadev-lad.rj@bp.renesas.com/

Cheers,
Prabhakar

>         M.
>
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > ---
> >  drivers/gpio/gpiolib.c | 9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > index b7694171655c..d36c4a965efc 100644
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -1187,15 +1187,18 @@ static void gpiochip_hierarchy_setup_domain_ops(struct irq_domain_ops *ops)
> >       ops->activate = gpiochip_irq_domain_activate;
> >       ops->deactivate = gpiochip_irq_domain_deactivate;
> >       ops->alloc = gpiochip_hierarchy_irq_domain_alloc;
> > -     ops->free = irq_domain_free_irqs_common;
> >
> >       /*
> > -      * We only allow overriding the translate() function for
> > +      * We only allow overriding the translate() and free() functions for
> >        * hierarchical chips, and this should only be done if the user
> > -      * really need something other than 1:1 translation.
> > +      * really need something other than 1:1 translation for translate()
> > +      * callback and free if user wants to free up any resources which
> > +      * were allocated during callbacks, for example populate_parent_alloc_arg.
> >        */
> >       if (!ops->translate)
> >               ops->translate = gpiochip_hierarchy_irq_domain_translate;
> > +     if (!ops->free)
> > +             ops->free = irq_domain_free_irqs_common;
> >  }
> >
> >  static int gpiochip_hierarchy_add_domain(struct gpio_chip *gc)
> > --
> > 2.25.1
> >
> >
>
> --
> Without deviation from the norm, progress is not possible.