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

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Message-ID: <20220503220550.3jczn2hzc5me34qj@pali>
Date:   Wed, 4 May 2022 00:05:50 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Tzung-Bi Shih <tzungbi@...nel.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        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 Monday 02 May 2022 21:37:16 Guenter Roeck wrote:
> On 5/2/22 20:57, Tzung-Bi Shih wrote:
> > 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().
> > 
> 
> Actually, that doesn't work at all. spin_lock() directly contradicts
> with gpiod_set_value_cansleep().
> 
> > > +	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()?
> 

Hello! I'm going to look at all these issues. Recently I sent max63
watchdog driver also into U-Boot and seems that I mixed DTS and driver
code between U-Boot and Kernel... and tested something mixed.

I will do new testing again, and will check that I'm testing correct
code.