linux-kernel - Re: [PATCH v6 3/3] pinctrl: Add Xilinx ZynqMP pinctrl driver support

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Message-ID: <CAHp75VfugGqLNU8LKJ_K3dPr=-eh6LHx75eV=33jH9OnryBoGA@mail.gmail.com>
Date:   Mon, 26 Apr 2021 17:04:42 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Sai Krishna Potthuri <lakshmis@...inx.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Michal Simek <michals@...inx.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        git <git@...inx.com>,
        "saikrishna12468@...il.com" <saikrishna12468@...il.com>
Subject: Re: [PATCH v6 3/3] pinctrl: Add Xilinx ZynqMP pinctrl driver support

On Mon, Apr 26, 2021 at 4:20 PM Sai Krishna Potthuri
<lakshmis@...inx.com> wrote:
> > From: Andy Shevchenko <andy.shevchenko@...il.com>
> > Sent: Friday, April 23, 2021 9:24 PM
> > On Thu, Apr 22, 2021 at 11:31 AM Sai Krishna Potthuri
> > <lakshmi.sai.krishna.potthuri@...inx.com> wrote:

...

> > > +config PINCTRL_ZYNQMP
> > > +       tristate "Pinctrl driver for Xilinx ZynqMP"
> > > +       depends on ZYNQMP_FIRMWARE
> > > +       select PINMUX
> > > +       select GENERIC_PINCONF
> > > +       default ZYNQMP_FIRMWARE
> > > +       help
> > > +         This selects the pinctrl driver for Xilinx ZynqMP platform.
> > > +         This driver will query the pin information from the firmware
> > > +         and allow configuring the pins.
> > > +         Configuration can include the mux function to select on those
> > > +         pin(s)/group(s), and various pin configuration parameters
> > > +         such as pull-up, slew rate, etc.
> >
> > Missed module name.
> Is this (module name) a configuration option in Kconfig?

It's a text in a free form that sheds light on how the module will be
named in case the user will choose "m".

...

> > > + * Copyright (C) 2020 Xilinx, Inc.
> >
> > 2021?
> Couple of versions for this patch series sent in 2020, hence maintaining
> the same.
> Is it like we maintain the year when this patch series is applied, which is
> 2021?

2020, 2021 sounds okay as well.

...

> > > +       if (pin >= zynqmp_desc.npins)
> > > +               return -EOPNOTSUPP;
> >
> > Is it possible?
> This is a safe check.

I.o.w. dead code, right?

> Pin information will get from dt files/Xilinx firmware (query pin information
> for a group)/user application and there are chances of getting wrong pin.

I'm not sure I understand this. How comes that pin control core will
ask for a pin higher than npins?

...

> > > +               ret = zynqmp_pm_pinctrl_get_config(pin, param, &arg);
> > > +               if (arg != PM_PINCTRL_BIAS_PULL_UP)
> > > +                       return -EINVAL;
> >
> > Error code being shadowed. Instead check it here properly.

> Are you mentioning the case where ret is also a non-zero?
> If yes, then I will update this check to
> if (!ret && arg != PM_PINCTRL_BIAS_PULL_UP)
>         return -EINVAL;

No, this is wrong in the same way.

> ret non-zero case, we are handling at the end of switch case.

I meant that you need to pass the real return code to the (upper) caller.
Ditto for all other cases (mentioned and not mentioned)

...

> > > +                       ret = -EOPNOTSUPP;
> >
> > Isn't it ENOTSUP for all cases here?
> Giving 'Operation Not Supported (EOPNOTSUPP)' error, when
> driver gets a request for unsupported pin or configuration.
> Can you please elaborate your question if I didn't answer properly.

The pin control subsystem along with the GPIO library are using
-ENOTSUPP error code for internal operations.
EOPNOTSUPP is the one that should be returned to user space. Is it the
case here?

...

> > > +};
> >
> > > +
> >
> > Ditto.
> I see some drivers are maintaining the extra line in above two cases.
> We shouldn't maintain extra line after struct declaration?

What's the point to add more blank lines where they won't add any value?

> > > +module_platform_driver(zynqmp_pinctrl_driver);

-- 
With Best Regards,
Andy Shevchenko