linux-kernel - Re: [PATCH v3 2/2] Add GPIO support for Realtek DHC(Digital Home Center) RTD SoCs.

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Date:   Thu, 14 Dec 2023 16:49:27 +0200
From:   Andy Shevchenko <andy@...nel.org>
To:     Michael Walle <michael@...le.cc>
Cc:     TY_Chang[張子逸] <tychang@...ltek.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-gpio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] Add GPIO support for Realtek DHC(Digital Home
 Center) RTD SoCs.

On Thu, Dec 14, 2023 at 03:35:18PM +0100, Michael Walle wrote:

> > > >> >> This driver enables configuration of GPIO direction, GPIO values,
> > > >> >> GPIO debounce settings and handles GPIO interrupts.
> > > >> >
> > > >> >Why gpio-regmap can't be used?
> > > >>
> > > >> I will try to use gpio-remap in the next version.
> > > >
> > > >If it appears that it makes code uglier / complicated, please add the note
> > > >somewhere to answer the above question.
> > > 
> > > I've traced the gpio-regmap.c file. It appears that for the driver
> > > to register
> > > gpio_irq_chip, it must create the irq_domain and add it into
> > > gpio_regmap_config.
> > > Additionally, the driver needs to register the irq handler by itself.
> > > However, this process can be managed by the gpiolib if the driver
> > > fills in the struct
> > > gpio_irq_chip inside struct gpio_chip before invoking
> > > gpiochip_add_data.
> > 
> > Hmm... I thought this is solvable issue.
> > Michael, is there a limitation in GPIO regmap that this driver can't be
> > converted?
> 
> gpio-regmap is designed that regmap-irq (drivers/base/regmap/irq.c) can be
> used. So, if regmap-irq fit this driver, then it can be used together with
> gpio-regmap.
> 
> From a quick glance at the patch, it looks like the gpio portion might fit
> gpio-regmap.
> 
> > > Moreover, apart from managing the registers for gpio direction and
> > > value, there
> > > are several other registers that require access(interrupt enable,
> > > debounce...).
> > > The GPIO IRQ status registers are located at different base
> > > addresses and are
> > > not contiguous. It may need to create an additional regmap and
> > > assign the access
> > > table to this regmap.
> > 
> > AFAIK this is not a problem as you can provide your own xlate function
> > that
> > will take care about register mapping.
> 
> Just for the gpio part. IIRC regmap has it own translation (regmap fields).
> 
> > > With the above consideration, I tend to keep using the existing
> > > method.
> > 
> > I would like to hear from Michael if it's indeed a big obstacle.
> 
> So, regarding the irq portion, again, it must fit the regmap-irq. For the
> additional requirement to set the debounce, you can add a .set_config to
> gpio_regmap_config and supply your own set_config callback. See also [1].

Thank you, Michael, for the prompt answer. It's insightful to me, I will try to
remember these aspects for the future reviews.

> [1]
> https://lore.kernel.org/linux-gpio/d4a6a640c373b6d939e147691efa596c@walle.cc/

-- 
With Best Regards,
Andy Shevchenko