linux-kernel - Re: [PATCH v2] gpio: mmio: handle "ngpios" properly in bgpio

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Date:   Sat, 25 Feb 2023 00:39:45 +0200
From:   andy.shevchenko@...il.com
To:     Asmaa Mnebhi <asmaa@...dia.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] gpio: mmio: handle "ngpios" properly in bgpio_init()

Fri, Feb 24, 2023 at 09:31:23PM +0000, Asmaa Mnebhi kirjoitti:

...

> > The problem with this change is that you need to provide bgpio_bits.
> > 
> > So, if there is a property when bgpio_bits will be updated?
> > 
> > That's said what you need is something like this:
> > 1) split "ngpios" handling code (lines ~718-744 in gpiolib.c)  into a helper
> > function that is available inside drivers/gpio;
> > 2) use it in bgpio_init() by overriding bgpio_bits.
> > 
> > ret = new_helper();
> > if (ret)
> >     gc->bgpio_bits = sz * 8;
> > else
> >     ... = gc->ngpio;
> 
> So this new_helper() which reads the ngpios property, would be called from
> bgpio_init() and From gpiochip_add_data_with_key() correct? Since there are
> some drivers that don’t use bgpio_init().

Correct.

> Also, shouldn't "gc->bgpio_bits = = sz * 8;" be independent of new_helper()

Nope. You need to link them anyway.

> function?  "bgpio_bits" is described as "number of register bits used for a
> generic GPIO i.e. <register width> * 8" which seems different from "ngpio"
> described as "the number of GPIOs handled by this controller"

But you are right, this should be = round_up(gc->ngpio, 8); to match the logic
with sz.

-- 
With Best Regards,
Andy Shevchenko