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From: Andy Shevchenko <andy.shevchenko@gmail.com>
Date: Mon, 22 Apr 2024 11:16:31 +0300
Message-ID: <CAHp75VfMb_=XKoQNbbVphLg-eQgc6eJbZOW36g_hU=-iK2bSOQ@mail.gmail.com>
Subject: Re: [PATCH v7 3/3] pinctrl: nuvoton: Add ma35d1 pinctrl and GPIO driver
To: Jacky Huang <ychuang570808@gmail.com>
Cc: linus.walleij@linaro.org, robh+dt@kernel.org, 
	krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org, 
	p.zabel@pengutronix.de, j.neuschaefer@gmx.net, 
	linux-arm-kernel@lists.infradead.org, linux-gpio@vger.kernel.org, 
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, 
	ychuang3@nuvoton.com, schung@nuvoton.com
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On Mon, Apr 22, 2024 at 7:10=E2=80=AFAM Jacky Huang <ychuang570808@gmail.co=
m> wrote:
> On 2024/4/10 =E4=B8=8B=E5=8D=88 04:54, Andy Shevchenko wrote:

..

> >> +#define MA35_GP_MODE_MASK_WIDTH              2
> >> +
> >> +#define MA35_GP_SLEWCTL_MASK_WIDTH   2
> > I looked at the code how you use these... Oh, please switch to FIELD_GE=
T() /
> > FIELD_PREP() (don't forget to include bitfield.h)
> >
> > ...
> >
> > ...
> >> +             regval &=3D ~GENMASK(setting->shift + MA35_MFP_BITS_PER_=
PORT - 1,
> >> +                                setting->shift);
> > This will generate an awful code. Use respective FIELD_*() macros.
> >
> > ...
> >
> >> +     regval &=3D ~GENMASK(gpio * MA35_GP_MODE_MASK_WIDTH - 1,
> >> +                        gpio * MA35_GP_MODE_MASK_WIDTH);
> >> +     regval |=3D mode << gpio * MA35_GP_MODE_MASK_WIDTH;
> > Ditto.
> >
> > ...
> >
> >> +     regval &=3D GENMASK(gpio * MA35_GP_MODE_MASK_WIDTH - 1,
> >> +                       gpio * MA35_GP_MODE_MASK_WIDTH);
> >> +
> >> +     return regval >> gpio * MA35_GP_MODE_MASK_WIDTH;
> > Ditto.

..

> Allow me to remove irrelevant parts.
>
> I attempted to follow your advice and use FIELD_GET() and FIELD_PREP(),
> but found
> it impractical. The reason is that these two macros require their 'mask'
> argument
> to be a constant, otherwise compilation errors occur, which is the issue
> I encountered.
> Since the mask here is calculated and not a constant, compilation errors
> occur.
>
> Taking MA35_GP_REG_MODE as an example, within 32 bits, every 2 bits
> represent
> the mode of a GPIO pin, and the mask is obtained by GENMASK(gpio * 2 -1,
> gpio * 2),

This is not good for the compiler, it can't figure out (at least in
some _supported_ by Linux kernel versions on some architectures) that
GENMASK can be constant here just left-shifted by arbitrary bits.

> where the 'gpio' argument is a variable, not a constant, leading to
> compilation
> errors.
>
> Due to this reason, I will leave this part unchanged, or do you have any
> other suggestions?

If you need non-constant field_get()/field_prep(), add a new patch
that moves them from drivers/iio/temperature/mlx90614.c (and there are
more custom implementations:
https://elixir.bootlin.com/linux/latest/A/ident/field_get) to the
bitfield.h and use them in your code.

--=20
With Best Regards,
Andy Shevchenko