linux-kernel - Re: [RFC PATCH] of: platform: Skip mapping of interrupts in of_device

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Message-ID: <CA+V-a8vUCXQa38NmYu9znakcq4A=Uedyn8w5+hXQ_WKf58oHRQ@mail.gmail.com>
Date:   Thu, 9 Dec 2021 10:00:44 +0000
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [RFC PATCH] of: platform: Skip mapping of interrupts in of_device_alloc()

Hi Marc,

Thank you for the review.

On Thu, Dec 9, 2021 at 8:07 AM Marc Zyngier <maz@...nel.org> wrote:
>
> On 2021-12-09 00:10, Lad Prabhakar wrote:
> > of_device_alloc() in early boot stage creates a interrupt mapping if
> > there exists a "interrupts" property in the node.
> >
> > For hierarchical interrupt domains using "interrupts" property in the
> > node
> > bypassed the hierarchical setup and messed up the irq setup.
> >
> > This patch adds a check in of_device_alloc() to skip interrupt mapping
> > if
> > "not-interrupt-producer" property is present in the node. This allows
> > nodes to describe the interrupts using "interrupts" property.
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > ---
> > Hi All,
> >
> > Spawning from discussion [1], here is simple patch (not the ideal
> > probably
> > welcome for suggestions) from stopping the OF code from creating a map
> > for
> > the interrupts when using "interrupts" property.
> >
> > [1] https://lore.kernel.org/lkml/87pmqrck2m.wl-maz@kernel.org/
> >     T/#mbd1e47c1981082aded4b32a52e2c04291e515508
> >
> > Cheers,
> > Prabhakar
> > ---
> >  drivers/of/platform.c | 13 ++++++++++---
> >  1 file changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> > index b3faf89744aa..629776ca1721 100644
> > --- a/drivers/of/platform.c
> > +++ b/drivers/of/platform.c
> > @@ -114,7 +114,7 @@ struct platform_device *of_device_alloc(struct
> > device_node *np,
> >                                 struct device *parent)
> >  {
> >       struct platform_device *dev;
> > -     int rc, i, num_reg = 0, num_irq;
> > +     int rc, i, num_reg = 0, num_irq = 0;
> >       struct resource *res, temp_res;
> >
> >       dev = platform_device_alloc("", PLATFORM_DEVID_NONE);
> > @@ -124,7 +124,14 @@ struct platform_device *of_device_alloc(struct
> > device_node *np,
> >       /* count the io and irq resources */
> >       while (of_address_to_resource(np, num_reg, &temp_res) == 0)
> >               num_reg++;
> > -     num_irq = of_irq_count(np);
> > +
> > +     /*
> > +      * we don't want to map the interrupts of hierarchical interrupt
> > domain
> > +      * into the parent domain yet. This will be the job of the
> > hierarchical
> > +      * interrupt driver code to map the interrupts as and when needed.
> > +      */
> > +     if (!of_property_read_bool(np, "not-interrupt-producer"))
>
> I don't think this is right. If anything, the expected behaviour should
> be
> indicated by the driver and not the device node.
>
> > +             num_irq = of_irq_count(np);
> >
> >       /* Populate the resource table */
> >       if (num_irq || num_reg) {
> > @@ -140,7 +147,7 @@ struct platform_device *of_device_alloc(struct
> > device_node *np,
> >                       rc = of_address_to_resource(np, i, res);
> >                       WARN_ON(rc);
> >               }
> > -             if (of_irq_to_resource_table(np, res, num_irq) != num_irq)
> > +             if (num_irq && of_irq_to_resource_table(np, res, num_irq) !=
> > num_irq)
> >                       pr_debug("not all legacy IRQ resources mapped for %pOFn\n",
> >                                np);
> >       }
>
> The root of the issue is that all the resource allocation is done
> upfront,
> way before we even have a driver that could potentially deal with this
> device. This is a potential waste of resource, and it triggers the
> issue you noticed.
>
> If you delay the resource allocation until there is an actual match with
> a
> driver, you could have a per-driver flag telling you whether the IRQ
> allocation should be performed before the probe() function is called.
>
As suggested by Rob, if we switch the drivers to use
platform_get_resource(pdev, IORESOURCE_IRQ, n) call with
platform_get_irq() this code should go away and with this switch the
resource allocation will happen demand. Is this approach OK?

Cheers,
Prabhakar

>          M.
> --
> Jazz is not dead. It just smells funny...