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 15:35:18 +0100
From:   Michael Walle <michael@...le.cc>
To:     Andy Shevchenko <andy@...nel.org>,
        TY_Chang[張子逸] <tychang@...ltek.com>
Cc:     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.

Hi,

>> >> >> 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].

-michael

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