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

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Date: Fri, 15 Dec 2023 06:50:32 +0000
From: TY_Chang[張子逸] <tychang@...ltek.com>
To: Andy Shevchenko <andy@...nel.org>, Michael Walle <michael@...le.cc>
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" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...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 Andy,

>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@wa
>> lle.cc/
>

I have looked into regmap-irq, it appears that using the default irq
thread_fn(regmap_irq_thread) is required. However, due to hardware limitation,
we need to inspect the IRQ_TYPE to determine whether to manage the irq within
the irq handler. I think our irq portion does not perfectly fit the regmap-irq.
Moreover, it seems that the gpio-regmap.c file needs to be modified if the GPIO driver
requires debounce settings. I think the gpio-regmap may not be appropriate for our driver.
Do you have any suggestions?

Thanks,
Tzuyi Chang