linux-kernel - Re: [PATCH v4 06/11] gpio: add support for the sl28cpld GPIO controller

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Date:   Fri, 5 Jun 2020 16:15:25 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Michael Walle <michael@...le.cc>
Cc:     "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-hwmon@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-watchdog@...r.kernel.org,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Lee Jones <lee.jones@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <maz@...nel.org>, Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v4 06/11] gpio: add support for the sl28cpld GPIO
 controller

On Fri, Jun 05, 2020 at 02:42:53PM +0200, Michael Walle wrote:
> Am 2020-06-05 14:00, schrieb Andy Shevchenko:
> > On Fri, Jun 5, 2020 at 12:14 AM Michael Walle <michael@...le.cc> wrote:

> > > +       return devm_regmap_add_irq_chip_np(dev, dev_of_node(dev),
> > > regmap,
> > 
> > It seems regmap needs to be converted to use fwnode.
> 
> Mhh, this _np functions was actually part of this series in the
> beginning.

Then, please, make them fwnode aware rather than OF centric.

> > > IRQF_ONESHOT, 0,
> > > +                                          irq_chip, &gpio->irq_data);

...

> > > +       dev_id = platform_get_device_id(pdev);
> > > +       if (dev_id)
> > > +               type = dev_id->driver_data;
> > 
> > Oh, no. In new code we don't need this. We have facilities to provide
> > platform data in a form of fwnode.
> 
> Ok I'll look into that.
> 
> But I already have a question, so there are of_property_read_xx(), which
> seems to be the old functions, then there is device_property_read_xx() and
> fwnode_property_read_xx(). What is the difference between the latter two?

It's easy. device_*() requires struct device to be established for this, so,
operates only against devices, while the fwnode_*() operates on pure data which
might or might not be related to any devices. If you understand OF examples
better, consider device node vs. child of such node.

...

> > > +       if (irq_support &&
> > 
> > Why do you need this flag? Can't simple IRQ number be sufficient?
> 
> I want to make sure, the is no misconfiguration. Eg. only GPIO
> flavors which has irq_support set, have the additional interrupt
> registers.

In gpio-dwapb, for example, we simple check two things: a) hardware limitation
(if IRQ is assigned to a proper port) and b) if there is any IRQ comes from DT,
ACPI, etc.

> > > +           device_property_read_bool(&pdev->dev,
> > > "interrupt-controller")) {
> > > +               irq = platform_get_irq(pdev, 0);
> > > +               if (irq < 0)
> > > +                       return irq;
> > > +
> > > +               ret = sl28cpld_gpio_irq_init(&pdev->dev, gpio, regmap,
> > > +                                            base, irq);
> > > +               if (ret)
> > > +                       return ret;
> > > +
> > > +               config.irq_domain =
> > > regmap_irq_get_domain(gpio->irq_data);
> > > +       }

...

> > > +       { .compatible = "kontron,sl28cpld-gpio",
> > > +         .data = (void *)SL28CPLD_GPIO },
> > > +       { .compatible = "kontron,sl28cpld-gpi",
> > > +         .data = (void *)SL28CPLD_GPI },
> > > +       { .compatible = "kontron,sl28cpld-gpo",
> > > +         .data = (void *)SL28CPLD_GPO },
> > 
> > All above can be twice less LOCs.
> 
> They are longer than 80 chars. Or do I miss something?

We have 100 :-)

...

> > > +               .name = KBUILD_MODNAME,
> > 
> > This actually not good idea in long term. File name can change and break
> > an ABI.
> 
> Ahh an explanation, why this is bad. Ok makes sense, although to be fair,
> .id_table should be used for the driver name matching. I'm not sure if
> this is used somewhere else, though.

I saw in my practice chain of renames for a driver. Now, if somebody
somewhere would like to instantiate a platform driver by its name...
Oops, ABI breakage.

And of course using platform data for such device makes less sense.

-- 
With Best Regards,
Andy Shevchenko