Re: [PATCH v1 12/16] pinctrl: starfive: Add pinctrl driver for StarFive SoCs

Andy Shevchenko
2021-10-13T16:58:34Z

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@gmail.com> wrote:
> > On Tue, Oct 12, 2021 at 4:43 PM Emil Renner Berthing <kernel@esmil.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