linux-kernel - Re: [PATCH 2/3] i2c: sh_mobile: Use platform_get_irq

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Message-ID: <CAMuHMdVxcjJtcBoMCYAZyGCcLAmxeN=mWJSyJ+g9bHjJ1kYrPw@mail.gmail.com>
Date:   Mon, 20 Dec 2021 13:54:09 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Rob Herring <robh+dt@...nel.org>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Chris Brandt <chris.brandt@...esas.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Linux I2C <linux-i2c@...r.kernel.org>,
        linux-rpi-kernel <linux-rpi-kernel@...ts.infradead.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux-sh list <linux-sh@...r.kernel.org>
Subject: Re: [PATCH 2/3] i2c: sh_mobile: Use platform_get_irq_optional() to
 get the interrupt

Hi Prabhakar,

On Mon, Dec 20, 2021 at 12:56 PM Lad, Prabhakar
<prabhakar.csengg@...il.com> wrote:
> On Mon, Dec 20, 2021 at 10:18 AM Geert Uytterhoeven
> <geert@...ux-m68k.org> wrote:
> > On Sat, Dec 18, 2021 at 5:59 PM Lad Prabhakar
> > <prabhakar.mahadev-lad.rj@...renesas.com> wrote:
> > > platform_get_resource(pdev, IORESOURCE_IRQ, ..) relies on static
> > > allocation of IRQ resources in DT core code, this causes an issue
> > > when using hierarchical interrupt domains using "interrupts" property
> > > in the node as this bypasses the hierarchical setup and messes up the
> > > irq chaining.
> >
> > Thanks for your patch!
> >
> > > In preparation for removal of static setup of IRQ resource from DT core
> > > code use platform_get_irq_optional() for DT users only.
> >
> > Why only for DT users?
> > Plenty of driver code shared by Renesas ARM (DT-based) on SuperH
> > (non-DT) SoCs already uses platform_get_irq_optional(), so I expect
> > that to work for both.
> >
> For the non DT users the IRQ resource is passed as a range [0] and not
> a single interrupt so I went with this approach. Is there a way I'm
> missing where we could still use platform_get_irq_xyz() variants for
> such cases?

Oh, I didn't realize it used a single resource with a range.
Is this common, i.e. would it make sense to add support for this to
platform_get_irq_optional()?

> > > --- a/drivers/i2c/busses/i2c-sh_mobile.c
> > > +++ b/drivers/i2c/busses/i2c-sh_mobile.c

> > > +                       if (irq <= 0 && irq != -ENXIO)
> > > +                               return irq ? irq : -ENXIO;
> >
> > Can irq == 0 really happen?
> >
> > All SuperH users of the "i2c-sh_mobile" platform device use an
> > evt2irq() value that is non-zero.
> >
> > I might have missed something, but it seems the only user of IRQ 0 on
> > SuperH is smsc911x Ethernet in arch/sh/boards/board-apsh4a3a.c and
> > arch/sh/boards/board-apsh4ad0a.c, which use evt2irq(0x200).
> >
> I'll keep that in mind if the Ethernet driver falls in the convection
> patch changes.

The Ethernet driver was converted 6 years ago, cfr. commit
965b2aa78fbcb831 ("net/smsc911x: fix irq resource allocation failure").

> [0] https://elixir.bootlin.com/linux/v5.16-rc6/source/arch/sh/kernel/cpu/sh4a/setup-sh7724.c#L454

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds