Message-ID: <YWc5zq0Moz3asWEa@smile.fi.intel.com>
Date:   Wed, 13 Oct 2021 22:55:58 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Emil Renner Berthing <kernel@...il.dk>
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>,
        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>,
        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 v1 12/16] pinctrl: starfive: Add pinctrl driver for
 StarFive SoCs

On Wed, Oct 13, 2021 at 06:38:14PM +0200, Emil Renner Berthing wrote:
> On Tue, 12 Oct 2021 at 19:03, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> > On Tue, Oct 12, 2021 at 4:43 PM Emil Renner Berthing <kernel@...il.dk> wrote:

...

> > > +free_pinmux:
> > > +       devm_kfree(dev, pinmux);
> > > +free_pins:
> > > +       devm_kfree(dev, pins);
> > > +free_grpname:
> > > +       devm_kfree(dev, grpname);
> >
> > What the heck?!
> 
> Just to be clear. You mean we don't need to explicitly free them
> because they're tied to the device right? I don't think the device
> will go away just because a single device tree entry can't be parsed,
> so on such errors this garbage would be left behind. You can still
> argue we shouldn't optimize for broken device trees, I just want to
> make it at conscious decision.

If you are using devm_kfree() it is quite likely shows either of the following
issues:

* you mustn't use devm_*() in the first place due to object lifetime;
* you shouldn't use devm_kfree() since this is the whole point of devm.

> > > +free_pgnames:
> > > +       devm_kfree(dev, pgnames);
> >
> > Ditto.

...

> > > +out:
> >
> > Useless label.
> 
> Hmm.. my compiler disagrees.

The comment implies that you return directly instead of using `goto out;`.

> > > +       return ret;

...

> > > +               v = pinmux[i];
> > > +               dout = ((v & BIT(7)) << (31 - 7)) | ((v >> 24) & 0xffU);
> > > +               doen = ((v & BIT(6)) << (31 - 6)) | ((v >> 16) & 0xffU);
> > > +               din  = (v >> 8) & 0xffU;
> >
> > What is this voodoo for?
> 
> In order to do pinmux we need the following pieces of information from
> the device tree for each pin ("GPIO" they call it):
> 
> output signal: 0-133 + 1bit reverse flag
> output enable signal: 0-133 + 1bit reverse flag
> optional input signal: 0-74 + special "none" value, right now 0xff
> gpio number: 0-63
> 
> As the code is now all that info is packed into a u32 for each pin
> using the GPIOMUX macro defined in the dt-binding header added in
> patch 10. There is also a diagram for how this packing is done. The
> above voodoo is for unpacking that.
> 
> I'd very much like to hear if you have a better solution for how to
> convey that information from the device tree to here.

At very least this code should have something like above in the comment.

...

> > > +               if (din != 0xff)
> > > +                       reg_din = sfp->base + GPIO_IN_OFFSET + 4 * din;
> > > +               else
> > > +                       reg_din = NULL;
> >
> > This looks like you maybe use gpio-regmap instead?
> 
> This was discussed at length when Drew sent in the GPIO part of this code:
> https://lore.kernel.org/linux-riscv/20210701002037.912625-1-drew@beagleboard.org/
> The conclusion was that because pinmux and controlling the pins from
> software in GPIO mode uses the same registers it is better to do a
> combined driver like this that can share the lock among other things.

And what does prevent exactly to base the GPIO part on gpio-regmap?

...

> > > +static const unsigned char starfive_drive_strength[] = {
> > > +       14, 21, 28, 35, 42, 49, 56, 63,
> >
> > Why table? Can you simply use the formula?!
> 
> Heh, yeah. So these are rounded values from a table and I never
> noticed that after rounding they follow a nice arithmetic progression.
> It'll probably still be nice to have an explanation in the comments
> about the formula then.

Yup!

> > > +};

...

> > > +               irq_set_handler_locked(d, handle_bad_irq);
> >
> > Why is this here? Move it to ->probe().
> 
> My thinking was that if something tries to set a an unsupported irq
> type, we should make sure the caller doesn't get spurious interrupts
> because we left the handler at its old value.

You already assigned to this handler in the ->probe(), what's this then?

...

> > > +               if (value <= 6)
> > > +                       writel(value, sfp->padctl + IO_PADSHARE_SEL);
> > > +               else
> >
> > > +                       dev_err(dev, "invalid signal group %u\n", value);
> >
> > Why _err if you not bail out here?
> 
> My thinking was that if the device tree specifies an invalid signal
> group we should just leave the setting alone and not break booting,
> but still be loud about it. Maybe that's too lenient and it's better
> to crash and burn immediately if someone does that.

Here is inconsistency between level of the message and following action.
There are (rare!) cases when it's justified, but I believe it's not the
case here. You have two choices or justify why you have to use error
level without stopping process.

...

All uncommented stuff you agreed on, correct?

-- 
With Best Regards,
Andy Shevchenko

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