linux-kernel - RE: [PATCH v4 1/2] gpio: gpio-mlxbf3: Add gpio driver support

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Date:   Thu, 23 Feb 2023 19:08:47 +0000
From:   Asmaa Mnebhi <asmaa@...dia.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
CC:     "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "bgolaszewski@...libre.com" <bgolaszewski@...libre.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: RE: [PATCH v4 1/2] gpio: gpio-mlxbf3: Add gpio driver support

> > > +       npins = MLXBF3_GPIO_MAX_PINS_PER_BLOCK;
> > > +       device_property_read_u32(dev, "npins", &npins);
> >
> > I don't see DT bindings for this property (being added in this series). Is it
> already established one?
> >
> > Ah that’s my bad. The property should be called "ngpios" like in the DT
> documentation. Will fix.
> 
> And why do you need it? What's a corner case that the GPIO library doesn't
> handle yet?

We have 2 gpiochips, gpiochip 0 supports 32 gpio pins and gpiochip 1 supports only 24 pins.
If I remove the logic from gpio-mlxbf3.c, the gpiolib.c logic will correctly set the ngpios = 32 for gpiochip 0 but will wrongly set ngpios=32 for gpiogchip 1:

gpiochip_add_data_with_key {
	[...]
	ngpios = gc->ngpio;
	if (ngpios == 0) {
		ret = device_property_read_u32(&gdev->dev, "ngpios", &ngpios);
		if (ret == -ENODATA)
			/*
			 * -ENODATA means that there is no property found and
			 * we want to issue the error message to the user.
			 * Besides that, we want to return different error code
			 * to state that supplied value is not valid.
			 */
			ngpios = 0;
		else if (ret)
			goto err_free_dev_name;

		gc->ngpio = ngpios;
	}
	[...]
}

bgpio_init {
	gc->bgpio_bits = sz * 8;
	gc->ngpio = gc->bgpio_bits;
}