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

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Date:   Fri, 05 Jun 2020 20:44:52 +0200
From:   Michael Walle <michael@...le.cc>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
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

Am 2020-06-05 15:15, schrieb Andy Shevchenko:
> 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.

ok

> 
>> > > 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.

Ahh thanks, got it.

> 
> ...
> 
>> > > +       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.

I can't follow you here. irq_support is like your (a); or the
"pp->idx == 0" in your example.

>> > > +           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 :-)

oh come on, since 6 days *g*

>> > > +               .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.

i just removed the id_table from all drivers anyways.

-michael