linux-kernel - Re: [PATCH 4/7] gpio: dwapb: Convert driver to using the GPIO-lib-based IRQ-chip

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Message-ID: <20200725000557.ru4h5twwd4ha4l6x@mobilestation>
Date:   Sat, 25 Jul 2020 03:05:57 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
CC:     Serge Semin <fancer.lancer@...il.com>,
        Hoan Tran <hoan@...amperecomputing.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Rob Herring <robh+dt@...nel.org>, <linux-gpio@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/7] gpio: dwapb: Convert driver to using the
 GPIO-lib-based IRQ-chip

On Thu, Jul 23, 2020 at 05:08:15PM +0300, Andy Shevchenko wrote:
> On Thu, Jul 23, 2020 at 04:38:55AM +0300, Serge Semin wrote:
> > GPIO-lib provides a ready-to-use interface to initialize an IRQ-chip on
> > top of a GPIO chip. It's better from maintainability and readability
> > point of view to use one instead of supporting a hand-written Generic
> > IRQ-chip-based implementation. Moreover the new implementation won't
> > cause much functional overhead but will provide a cleaner driver code.
> > All of that makes the DW APB GPIO driver conversion pretty much justified
> > especially seeing a tendency of the other GPIO drivers getting converted
> > too.
> > 
> > Here is what we do in the framework of this commit to convert the driver
> > to using the GPIO-lib-based IRQ-chip interface:
> > 1) IRQ ack, mask and unmask callbacks are locally defined instead of
> > using the Generic IRQ-chip ones.
> > 2) An irq_chip structure instance is embedded into the dwapb_gpio
> > private data. Note we can't have a static instance of that structure since
> > GPIO-lib will add some hooks into it by calling gpiochip_set_irq_hooks().
> > A warning about that would have been printed by the GPIO-lib code if we
> > used a single irq_chip structure instance for multiple DW APB GPIO
> > controllers.
> > 3) Initialize the gpio_irq_chip structure embedded into the gpio_chip
> > descriptor. By default there is no IRQ enabled so any event raised will be
> > handled by the handle_bad_irq() IRQ flow handler. If DW APB GPIO IP-core
> > is synthesized to have non-shared reference IRQ-lines, then as before the
> > hierarchical and cascaded cases are distinguished by checking how many
> > parental IRQs are defined. (Note irq_set_chained_handler_and_data() won't
> > initialize IRQs, which descriptors couldn't be found.) If DW APB GPIO IP
> > is used on a platform with shared IRQ line, then we simply won't let the
> > GPIO-lib to initialize the parental IRQs, but will handle them locally in
> > the driver.
> > 4) Discard linear IRQ-domain and Generic IRQ-chip initialization, since
> > GPIO-lib IRQ-chip interface will create a new domain and accept a standard
> > IRQ-chip structure pointer based on the setting we provided in the
> > gpio_irq_chip structure.
> > 5) Manually select a proper IRQ flow handler directly in the
> > irq_set_type() callback by calling irq_set_handler_locked() method, since
> > an ordinary (not Generic) irq_chip descriptor is now utilized.
> > 6) Discard the custom GPIO-to-IRQ mapping function since GPIO-lib defines
> > the standard method gpiochip_to_irq(), which will be used anyway no matter
> > whether the custom to_irq callback is specified or not.
> > 7) Discard the acpi_gpiochip_{request,free}_interrupts()
> > invocations, since they will be called from
> > gpiochip_add_irqchip()/gpiochip_irqchip_remove() anyway.
> > 8) Alter CONFIG_GPIO_DWAPB kernel config to select
> > CONFIG_GPIOLIB_IRQCHIP instead of CONFIG_GENERIC_IRQ_CHIP.
> 
> 
> ...
> 
> One more thing...
> 
> >  static u32 dwapb_do_irq(struct dwapb_gpio *gpio)
> >  {
> > +	struct gpio_chip *gc = &gpio->ports[0].gc;
> >  	unsigned long irq_status;
> >  	irq_hw_number_t hwirq;
> >  
> >  	irq_status = dwapb_read(gpio, GPIO_INTSTATUS);
> >  	for_each_set_bit(hwirq, &irq_status, 32) {
> > -		int gpio_irq = irq_find_mapping(gpio->domain, hwirq);
> > +		int gpio_irq = gc->to_irq(gc, hwirq);
> 

> Very, very few do this.
> Can we stick with the original one?
> (See plenty of other examples in the GPIO / pin control subsystems.

You are right. After more thorough studying the IRQ-domain code I've found out
that irq_domain_add_simple() provides the on-the-fly mapping creation. We
don't have to call irq_create_mapping() first before using irq_find_mapping().
So the irq_find_mapping(gc->irq.domain, hwirq) method can be freely called here
the same way as the most of the GPIO drivers do. Thanks for noticing this.

-Sergey

> 
> >  		u32 irq_type = irq_get_trigger_type(gpio_irq);
> >  
> >  		generic_handle_irq(gpio_irq);
> 
> 
> >  }
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>