linux-kernel - Re: [RFC PATH 2/2] gpio: starfive-jh7100: Add StarFive JH7100 GPIO driver

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Message-ID: <c915172ac456b3f7b7547c065c41750b@walle.cc>
Date:   Fri, 02 Jul 2021 16:59:51 +0200
From:   Michael Walle <michael@...le.cc>
To:     Drew Fustini <drew@...gleboard.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Michael Zhu <michael.zhu@...rfivetech.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Fu Wei <tekkamanninja@...il.com>, linux-kernel@...r.kernel.org,
        linux-gpio@...r.kernel.org, linux-riscv@...ts.infradead.org,
        devicetree@...r.kernel.org, Emil Renner Berthing <kernel@...il.dk>,
        Huan Feng <huan.feng@...rfivetech.com>
Subject: Re: [RFC PATH 2/2] gpio: starfive-jh7100: Add StarFive JH7100 GPIO
 driver

Hi Drew,

Am 2021-07-01 22:33, schrieb Drew Fustini:
> On Thu, Jul 01, 2021 at 08:39:40AM +0200, Michael Walle wrote:
>> Hi Drew,
>> 
>> Am 2021-07-01 02:20, schrieb Drew Fustini:
>> > Add GPIO driver for the StarFive JH7100 SoC [1] used on the
>> > BeagleV Starlight JH7100 board [2].
>> >
>> > [1] https://github.com/starfive-tech/beaglev_doc/
>> > [2] https://github.com/beagleboard/beaglev-starlight
>> >
>> > Signed-off-by: Emil Renner Berthing <kernel@...il.dk>
>> > Signed-off-by: Huan Feng <huan.feng@...rfivetech.com>
>> > Signed-off-by: Drew Fustini <drew@...gleboard.org>
>> 
>> Could this driver use GPIO_REGMAP and REGMAP_IRQ? See
>> drivers/gpio/gpio-sl28cpld.c for an example.
>> 
>> -michael
> 
> Thank you for the suggestion.  I am not familiar with GPIO_REGMAP and
> REGMAP_IRQ so I will read about it.  Is the advantage is that is helps
> to reduce code duplication by using an abstraction?

Yes, I've looked briefly at your patch and it seemed that GPIO_REGMAP
might fit here which will reduce code.

> I did notice that the gpio-sifive.c driver used regmap_update_bits() 
> and
> regmap_write().
> 
> I suppose that is better than writel_relaxed() and iowrite32() which
> this RFC driver does?

Its just another abstraction layer in between. For MMIO it will also
end up using some variant of the above (see regmap-mmio.c). But if you
use regmap, you can also use REGMAP_IRQ which might also be a fit
for your GPIO controller and thus don't have to implement your own
versions for the irq_chip ops.

-michael