linux-kernel - Re: [PATCH v1 2/2] counter: add GPIO based pulse counters

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Message-ID: <CAHp75VfnV+A=BpXGqf=xC=RTozfNrmq7X5V0o8aK2ptMyZF9YA@mail.gmail.com>
Date:   Thu, 21 Jan 2021 18:10:10 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Rob Herring <robh+dt@...nel.org>,
        William Breathitt Gray <vilhelm.gray@...il.com>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        David Jander <david@...tonic.nl>,
        Robin van der Gracht <robin@...tonic.nl>,
        linux-iio <linux-iio@...r.kernel.org>
Subject: Re: [PATCH v1 2/2] counter: add GPIO based pulse counters

On Thu, Jan 21, 2021 at 4:32 PM Oleksij Rempel <o.rempel@...gutronix.de> wrote:
>
> Add simple GPIO base pulse counter. This device is used to measure
> rotation speed of some agricultural devices, so no high frequency on the
> counter pin is expected.
>
> The maximal measurement frequency depends on the CPU and system load. On
> the idle iMX6S I was able to measure up to 20kHz without count drops.

...

> +#include <linux/of_gpio.h>

It would be better to see OF agnostic code WRT GPIOs.

...

> +static ssize_t gpio_pulse_count_enable_read(struct counter_device *counter,
> +                                           struct counter_count *count,
> +                                           void *private, char *buf)
> +{
> +       struct gpio_pulse_priv *priv = counter->priv;
> +
> +       return scnprintf(buf, PAGE_SIZE, "%d\n", priv->enabled);

sysfs_emit()

> +}
> +
> +static ssize_t gpio_pulse_count_enable_write(struct counter_device *counter,
> +                                            struct counter_count *count,
> +                                            void *private,
> +                                            const char *buf, size_t len)
> +{
> +       struct gpio_pulse_priv *priv = counter->priv;
> +       bool enable;
> +       ssize_t ret;
> +
> +       ret = kstrtobool(buf, &enable);
> +       if (ret)
> +               return ret;
> +
> +       if (priv->enabled == enable)
> +               return len;
> +
> +       if (enable)
> +               enable_irq(priv->irq);
> +       else
> +               disable_irq(priv->irq);

Oops, if IRQ happens here, shouldn't we have priv->enabled already set properly?

> +       priv->enabled = enable;
> +
> +       return len;
> +}
> +
> +static const struct counter_count_ext gpio_pulse_count_ext[] = {
> +       {
> +               .name = "enable",
> +               .read = gpio_pulse_count_enable_read,
> +               .write = gpio_pulse_count_enable_write

Leave the comma here.

> +       },
> +};

...

> +static struct counter_signal gpio_pulse_signals[] = {
> +       {
> +               .id = 0,
> +               .name = "Channel 0 signal"

Leave the comma.

> +       },
> +};
> +
> +static struct counter_synapse gpio_pulse_count_synapses[] = {
> +       {
> +               .actions_list = gpio_pulse_synapse_actions,
> +               .num_actions = ARRAY_SIZE(gpio_pulse_synapse_actions),
> +               .signal = &gpio_pulse_signals[0]

Ditto.

> +       },
> +};

...

> +static struct counter_count gpio_pulse_counts[] = {
> +       {
> +               .id = 0,
> +               .name = "Channel 1 Count",
> +               .functions_list = gpio_pulse_count_functions,
> +               .num_functions = ARRAY_SIZE(gpio_pulse_count_functions),
> +               .synapses = gpio_pulse_count_synapses,
> +               .num_synapses = ARRAY_SIZE(gpio_pulse_count_synapses),
> +               .ext = gpio_pulse_count_ext,
> +               .num_ext = ARRAY_SIZE(gpio_pulse_count_ext)

Ditto

> +       },
> +};
> +

...

> +       struct device_node *np = pdev->dev.of_node;

> +       if (of_gpio_count(np) != 1) {
> +               dev_err(dev, "Error, need exactly 1 gpio for device\n");
> +               return -EINVAL;
> +       }

gpiod_count() ?

> +       priv->gpio = devm_fwnode_gpiod_get(dev, of_fwnode_handle(np),
> +                                          NULL, GPIOD_IN, GPIO_PULSE_NAME);

of node to fwnode, can we avoid dragging this here to there?

Why is devm_gpiod_get() followed by a label setting not good enough?

> +       if (IS_ERR(priv->gpio))
> +               return dev_err_probe(dev, PTR_ERR(priv->gpio), "failed to get gpio\n");

...

> +static const struct of_device_id gpio_pulse_cnt_of_match[] = {
> +       { .compatible = "virtual,gpio-pulse-counter", },
> +       {},

No comma needed for real terminator entry.

> +};

-- 
With Best Regards,
Andy Shevchenko