linux-kernel - Re: [PATCH v3 12/16] pinctrl: starfive: Add pinctrl driver for StarFive SoCs

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Date:   Wed, 3 Nov 2021 13:35:23 +0100
From:   Emil Renner Berthing <kernel@...il.dk>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     linux-riscv <linux-riscv@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Sagar Kadam <sagar.kadam@...ive.com>,
        Drew Fustini <drew@...gleboard.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michael Zhu <michael.zhu@...rfivetech.com>,
        Fu Wei <tekkamanninja@...il.com>,
        Anup Patel <anup.patel@....com>,
        Atish Patra <atish.patra@....com>,
        Matteo Croce <mcroce@...rosoft.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Huan Feng <huan.feng@...rfivetech.com>
Subject: Re: [PATCH v3 12/16] pinctrl: starfive: Add pinctrl driver for
 StarFive SoCs

On Wed, 3 Nov 2021 at 10:13, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> On Tue, Nov 2, 2021 at 10:35 PM Emil Renner Berthing <kernel@...il.dk> wrote:
> > On Tue, 2 Nov 2021 at 21:02, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> > > On Tue, Nov 2, 2021 at 6:50 PM Emil Renner Berthing <kernel@...il.dk> wrote:
>
> > > > +       switch (trigger) {
>
> > > > +       default:
> > >
> > > > +               irq_set_handler_locked(d, handle_bad_irq);
> > >
> > > Why? You have it already in ->probe(), what's the point?
> >
> > So last time you asked about this, I explained a situation where
> > userspace first grabs a GPIO, set the interrupt to edge triggered, and
> > then later loads a driver that requests an unsupported IRQ type.
>
> I didn't get this scenario. Is it real?

No, it's totally made up, but I mean we even have tools like fuzzing
to help us find bugs that would never happen in real use cases.

> > Then
> > I'd like to set the handler back to handle_bad_irq so we don't get
> > weird interrupts, but maybe now you know a reason why that doesn't
> > matter or can't happen?
>
> In ->probe() you set _default_ handler to bad(), what do you mean by
> 'set the handler back to bad()'? How is it otherwise if you free an
> interrupt?

It might not be, but when not sure I thought it better to error on the
safe side.

> So, please elaborate with call traces what the scenario / use case you
> are talking about. If it's true what you are saying, we have a
> situation (plenty of GPIO drivers don't do what you are suggesting
> here).
>
> > > > +               return -EINVAL;
> > > > +       }
>
> ...
>
> > > > +       ret = reset_control_deassert(rst);
> > > > +       if (ret)
> > > > +               return dev_err_probe(dev, ret, "could not deassert resetd\n");
> > >
> > > > +       ret = devm_pinctrl_register_and_init(dev, &starfive_desc, sfp, &sfp->pctl);
> > > > +       if (ret)
> > >
> > > I don't see who will assert reset here.
> >
> > No, so originally this driver would first assert and then deassert
> > reset. I decided against that because in all likelyhood earlier boot
> > stages would have set pinmux up for a serial port, and we don't want
> > to interrupt the serial debug output. The only reason I make sure the
> > reset line is deasserted is in case someone makes a really minimal
> > bootloader that just does the absolute minimal to load a Linux kernel
> > and doesn't even log any anything.
> >
> > By the same token we also don't want to assert reset on error in case
> > it resets pin muxing for the the serial line that was supposed to log
> > the error.
>
> Perhaps comment in the code explaining this?

Sure.