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

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Message-ID: <CA+V-a8vNUhVBFNf-M6s1BmXbdCpdyJOx2g=t=QJf1jQzUA3xow@mail.gmail.com>
Date:   Thu, 9 Dec 2021 11:34:31 +0000
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Rob Herring <robh+dt@...nel.org>, Marc Zyngier <maz@...nel.org>
Cc:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        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 Rob and Marc,

On Thu, Dec 9, 2021 at 10:33 AM Marc Zyngier <maz@...nel.org> wrote:
>
> On Thu, 09 Dec 2021 10:00:44 +0000,
> "Lad, Prabhakar" <prabhakar.csengg@...il.com> wrote:
> >
> > > 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?
>
> If you get rid of of_irq_to_resource_table() altogether, then yes,
> this has a fighting chance to work.
>
Yes, switching to platform_get_irq() will eventually cause
of_irq_to_resource_table() to go away.

On second thought, instead of touching all the drivers, if we update
platform_get_resource/platform_get_resource_byname to internally call
platform_get_irq() internally if it's a IORESOURCE_IRQ resource. Does
that sound good or should I just get on changing all the drivers to
use platform_get_irq() instead?

Cheers,
Prabhakar

>         M.
>
>
> --
> Without deviation from the norm, progress is not possible.