linux-kernel - Re: [PATCH v3 4/7] drivers: leds: Add the iEi WT61P803 PUZZLE LED driver

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Message-ID: <CADZsf3ZL712nZh5nQxh5RQ=YCbM0fEK8dp-uHyOW+2FSMv+UpA@mail.gmail.com>
Date:   Tue, 6 Oct 2020 08:41:45 +0200
From:   Luka Kovacic <luka.kovacic@...tura.hr>
To:     Pavel Machek <pavel@....cz>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-hwmon@...r.kernel.org,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        Lee Jones <lee.jones@...aro.org>, Dan Murphy <dmurphy@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Andrew Lunn <andrew@...n.ch>,
        Jason Cooper <jason@...edaemon.net>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Marek Behun <marek.behun@....cz>,
        Luka Perkov <luka.perkov@...tura.hr>,
        Robert Marko <robert.marko@...tura.hr>
Subject: Re: [PATCH v3 4/7] drivers: leds: Add the iEi WT61P803 PUZZLE LED driver

On Wed, Sep 30, 2020 at 9:48 PM Pavel Machek <pavel@....cz> wrote:
>
> Hi!
>
> > +static int iei_wt61p803_puzzle_led_brightness_set_blocking(struct led_classdev *cdev,
> > +             enum led_brightness brightness)
> > +{
> > +     struct iei_wt61p803_puzzle_led *priv = cdev_to_iei_wt61p803_puzzle_led(cdev);
> > +     unsigned char *resp_buf = priv->response_buffer;
> > +     unsigned char led_power_cmd[5] = {
> > +             IEI_WT61P803_PUZZLE_CMD_HEADER_START,
> > +             IEI_WT61P803_PUZZLE_CMD_LED,
> > +             IEI_WT61P803_PUZZLE_CMD_LED_POWER,
> > +             (char)IEI_LED_OFF
> > +     };
> > +     size_t reply_size;
> > +
> > +     mutex_lock(&priv->lock);
> > +     if (brightness == LED_OFF) {
> > +             led_power_cmd[3] = (char)IEI_LED_OFF;
> > +             priv->led_power_state = LED_OFF;
> > +     } else {
> > +             led_power_cmd[3] = (char)IEI_LED_ON;
> > +             priv->led_power_state = LED_ON;
> > +     }
> > +     mutex_unlock(&priv->lock);
> > +
> > +     return iei_wt61p803_puzzle_write_command(priv->mcu, led_power_cmd,
> > +                     sizeof(led_power_cmd), resp_buf, &reply_size);
> > +}
>
> Is the mutex needed? If so, should it include the
> iei_wt61p803_puzzle_write_command()? Does
> iei_wt61p803_puzzle_write_command() have internal locking to prevent
> two messages from being mingled?
>
> Best regards,
>                                                                         Pavel
>
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Hello Pavel,

The mutex isn't needed and can be removed.
The function iei_wt61p803_puzzle_write_command() already handles its own
mutex locking, so a separate mutex isn't required.

Does brightness_set_blocking only block a single caller (each caller separately)
or does it block all callers until the previous caller is finished?

Kind regards,
Luka