linux-kernel - Re: [PATCH v2 10/10] pwm: Add Raspberry Pi Firmware based PWM bus

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Message-ID: <CAHp75VcB5oxXs38UH5taVGj21wUi3sHYdRPOj3wxa3yXg0vmUA@mail.gmail.com>
Date:   Thu, 22 Oct 2020 21:53:35 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        linux-pwm@...r.kernel.org,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        Stefan Wahren <wahrenst@....net>,
        linux-input <linux-input@...r.kernel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:STAGING SUBSYSTEM" <devel@...verdev.osuosl.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        linux-rpi-kernel <linux-rpi-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 10/10] pwm: Add Raspberry Pi Firmware based PWM bus

On Thu, Oct 22, 2020 at 9:05 PM Nicolas Saenz Julienne
<nsaenzjulienne@...e.de> wrote:
>
> Adds support to control the PWM bus available in official Raspberry Pi
> PoE HAT. Only RPi's co-processor has access to it, so commands have to
> be sent through RPi's firmware mailbox interface.

>  drivers/pwm/pwm-raspberrypi.c | 221 ++++++++++++++++++++++++++++++++++

Name is completely confusing.
Please, make it unique enough to understand that this is exactly the
device it serves for.

For example, pwm-rpi-poe is better.

...

> + *  - Only normal polarity

Can't it be emulated? Isn't it 100% - duty cycle % ?


> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>

...

> +       ret = rpi_firmware_property(firmware, RPI_FIRMWARE_SET_POE_HAT_VAL,
> +                                   &msg, sizeof(msg));
> +       if (ret)
> +               return ret;

> +       else if (msg.ret)

Redundant 'else'

> +               return -EIO;

...

> +       ret = rpi_firmware_property(firmware, RPI_FIRMWARE_GET_POE_HAT_VAL,
> +                                   &msg, sizeof(msg));
> +       if (ret)
> +               return ret;

> +       else if (msg.ret)

Ditto.

> +               return -EIO;

...

> +       firmware_node = of_get_parent(dev->of_node);
> +       if (!firmware_node) {
> +               dev_err(dev, "Missing firmware node\n");
> +               return -ENOENT;
> +       }
> +
> +       firmware = rpi_firmware_get(firmware_node);
> +       of_node_put(firmware_node);
> +       if (!firmware)
> +               return -EPROBE_DEFER;

Looks like a hack.

...

> +       ret = pwmchip_remove(&rpipwm->chip);
> +       if (!ret)
> +               rpi_firmware_put(rpipwm->firmware);
> +
> +       return ret;

Can't you use the usual pattern?

  ret = ...
  if (ret)
    return ret;
  ...
  return 0;

-- 
With Best Regards,
Andy Shevchenko