linux-kernel - Re: [PATCH 02/12] pinctrl: add a pincontrol driver for BCM6328

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Message-ID: <CACRpkdbxAQTft8dapGqBDxM8nbkPvK4i95ND0JBFb_riafZSSg@mail.gmail.com>
Date:   Tue, 2 Mar 2021 16:20:35 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Álvaro Fernández Rojas <noltari@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Jonas Gorski <jonas.gorski@...il.com>,
        Necip Fazil Yildiran <fazilyildiran@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/12] pinctrl: add a pincontrol driver for BCM6328

Hi Álvaro,

thanks for your patch!

On Thu, Feb 25, 2021 at 5:42 PM Álvaro Fernández Rojas
<noltari@...il.com> wrote:

> Add a pincontrol driver for BCM6328. BCM628 supports muxing 32 pins as
> GPIOs, as LEDs for the integrated LED controller, or various other
> functions. Its pincontrol mux registers also control other aspects, like
> switching the second USB port between host and device mode.
>
> Signed-off-by: Álvaro Fernández Rojas <noltari@...il.com>
> Signed-off-by: Jonas Gorski <jonas.gorski@...il.com>

Thanks for working on this. This SoC definitely need to come upstream.

I think this driver can be simplified a bit and reuse some core infrastructure
to make it more maintainable. It might be a bit of challenge but definitely
worth it!

> +config PINCTRL_BCM6328
> +       bool "Broadcom BCM6328 GPIO driver"
> +       depends on OF_GPIO && (BMIPS_GENERIC || COMPILE_TEST)
> +       select PINMUX
> +       select PINCONF
> +       select GENERIC_PINCONF
> +       select MFD_SYSCON
> +       default BMIPS_GENERIC
> +       help
> +          Say Y here to enable the Broadcom BCM6328 GPIO driver.

I suggest

select GPIO_REGMAP
select GPIOLIB_IRQCHIP
select IRQ_DOMAIN_HIERARCHY

see below.

(...)
> +#include <linux/bitops.h>

Just <linux/bits.h> maybe, if you only use BIT() and GENMASK().

> +#include <linux/gpio.h>
> +#include <linux/of_gpio.h>

Do not include these, just:
#include <linux/gpio/driver.h>

> +#define BCM6328_DIROUT_REG     0x04
> +#define BCM6328_DATA_REG       0x0c
> +#define BCM6328_MODE_REG       0x18

This looks very much like it could use GPIO_REGMAP.
Can you look at:
drivers/gpio/gpio-regmap.c
drivers/gpio/gpio-sl28cpld.c

And see if you can do what that driver is doing and reuse
this core infrastructure?

> +static inline unsigned int bcm6328_bank_pin(unsigned int pin)
> +{
> +       return pin % PINS_PER_BANK;
> +}

I am generally reluctant about registering several banks/instances
of the GPIO if it is possible to just use more devices in the
device tree, like one for each instance.

> +static inline unsigned int bcm6328_reg_off(unsigned int reg, unsigned int pin)
> +{
> +       return reg - (pin / PINS_PER_BANK) * BANK_SIZE;
> +}

Because it leads to this kind of weirdness to split out the devices
from the main device in practice.

> +static int bcm6328_gpio_direction_input(struct gpio_chip *chip,
> +                                       unsigned int pin)
> +{
(...)
> +       /*
> +        * Check with the pinctrl driver whether this pin is usable as
> +        * an input GPIO
> +        */
> +       ret = pinctrl_gpio_direction_input(chip->base + pin);
> +       if (ret)
> +               return ret;

This is very nice.

> +static int bcm6328_gpio_to_irq(struct gpio_chip *chip, unsigned gpio)
> +{
> +       char irq_name[7];
> +
> +       sprintf(irq_name, "gpio%d", gpio);
> +
> +       return of_irq_get_byname(chip->of_node, irq_name);
> +}

This is a clear indication that we are dealing with a hierarchical irqchip.

My assumption is that you have one IRQ per GPIO line, so each
GPIO has a dedicated IRQ on the interrupt controller. Correct?

This means:

- Do not add all the interrupts into the device tree by name.

- In Kconfig select GPIOLIB_IRQCHIP, select IRQ_DOMAIN_HIERARCHY

- Populate a simple struct gpio_irq_chip, if no local registers need
  updating on interrupts, just pass interrupts through
        .irq_mask       = irq_chip_mask_parent,
        .irq_unmask     = irq_chip_unmask_parent,
  etc.

- Implement bcm6328_gpio_child_to_parent_hwirq() for this chip
  with hardcoded mappings between the hardware GPIO and interrupt
  lines, using the parent interrupt controller hierarchically. This mapping
  is determined from the compatible-string, and part of the property
  of how the GPIO block is integrated with the SoC. If need be to
  tell different chips apart, more precise compatible strings are needed.

- Examples:
  drivers/gpio/gpio-ixp4xx.c
  drivers/gpio/gpio-sifive.c

If you do this you will notice the core is more helpful to cut down on the
code.

Yours,
Linus Walleij