linux-kernel - Re: [PATCH v2 2/2] watchdog: max63xx_wdt: Add support for specifying WDI logic via GPIO

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Message-ID: <YnCoQUGQsXIfbowQ@google.com>
Date:   Tue, 3 May 2022 11:57:53 +0800
From:   Tzung-Bi Shih <tzungbi@...nel.org>
To:     Pali Rohár <pali@...nel.org>
Cc:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Rob Herring <robh+dt@...nel.org>,
        linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] watchdog: max63xx_wdt: Add support for specifying
 WDI logic via GPIO

On Fri, Apr 29, 2022 at 03:13:49PM +0200, Pali Rohár wrote:
> @@ -27,6 +27,7 @@
>  #include <linux/io.h>
>  #include <linux/slab.h>
>  #include <linux/property.h>
> +#include <linux/gpio/consumer.h>

It would be better to keep them alphabetically.  Anyway, they aren't sorted
originally...

> +static void max63xx_gpio_ping(struct max63xx_wdt *wdt)
> +{
> +	spin_lock(&wdt->lock);

Does it really need to acquire the lock?  It looks like the lock is to prevent
concurrent accesses to the mmap in max63xx_mmap_ping() and max63xx_mmap_set().

> +	gpiod_set_value_cansleep(wdt->gpio_wdi, 1);
> +	udelay(1);

Doesn't it need to include <linux/delay.h> for udelay()?

> @@ -225,10 +240,19 @@ static int max63xx_wdt_probe(struct platform_device *pdev)
>  		return -EINVAL;
>  	}
>  
> +	wdt->gpio_wdi = devm_gpiod_get(dev, NULL, GPIOD_FLAGS_BIT_DIR_OUT);
> +	if (IS_ERR(wdt->gpio_wdi) && PTR_ERR(wdt->gpio_wdi) != -ENOENT)

Use devm_gpiod_get_optional() to make the intent clear.  Also, it gets rid of
the check for -ENOENT.

> +		return dev_err_probe(dev, PTR_ERR(wdt->gpio_wdi),
> +				     "unable to request gpio: %ld\n",
> +				     PTR_ERR(wdt->gpio_wdi));

It doesn't need to again print for PTR_ERR(wdt->gpio_wdi).  dev_err_probe()
prints the error.

>  	err = max63xx_mmap_init(pdev, wdt);
>  	if (err)
>  		return err;
>  
> +	if (!IS_ERR(wdt->gpio_wdi))
> +		wdt->ping = max63xx_gpio_ping;

Thus, the max63xx_gpio_ping() overrides max63xx_mmap_ping() if the GPIO was
provided?  It would be better to mention the behavior in the commit message.

Also, could both the assignments of `wdt->gpio_wdi` and `wdt->ping` happen
after max63xx_mmap_init()?