linux-kernel - Some problems with sysfs patch (was Re: [PATCH v6] watchdog: New watchdog driver for MEN A21 watchdogs)

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Date:	Thu, 6 Jun 2013 12:51:03 +0200
From:	Johannes Thumshirn <johannes.thumshirn@....de>
To:	Guenter Roeck <linux@...ck-us.net>, <wim@...ana.be>
CC:	<linux-watchdog@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<johannes.thumshirn@....de>
Subject: Some problems with sysfs patch (was Re: [PATCH v6] watchdog: New
 watchdog driver for MEN A21 watchdogs)

On Mon, Jun 03, 2013 at 11:50:26AM +0200, Johannes Thumshirn wrote:
> On Fri, May 31, 2013 at 09:15:23PM -0700, Guenter Roeck wrote:
> > On Fri, May 31, 2013 at 02:55:19PM +0200, Johannes Thumshirn wrote:
> > > Hi Guenther,
> > > On Fri, May 31, 2013 at 04:40:37AM -0700, Guenter Roeck wrote:
> > > > > +#define GPIO_WD_ENAB	169
> > > > > +#define GPIO_WD_FAST	170
> > > > > +#define GPIO_WD_TRIG	171
> > > > > +
> > > > > +#define GPIO_RST_CAUSE_BASE 166
> > > > > +
> > > >
> > > > I think I asked that before ... as you are supporting devicetree, gpio pins
> > > > should really be provided through devicetree properties and not be hardcoded.
> > > >
> > > Yes you did and I didn't come up with a solution to this problem yet. I understand
> > > and agree to your concerns but I'm lacking example code/documentation for it, maybe
> > > you can point me to an example on that and then I'll update my code accordingly.
> > >
> >
> > Have a look at Documentation/devicetree/bindings/gpio/gpio-fan.txt and
> > drivers/hwmon/gpio-fan.c.
>
> Thanks a lot, this really helped me out. Updated patch is comming today
> including the bindings document Arnd Bergmann requested. I only need to rebase
> the sysfs patch on top of that changes.
>
> Regards,
> Johannes

Regarding the sysfs patch, I have a funny effect in my (rebased) sysfs code.

Given the following code:

+static ssize_t rebootcause_show(struct device *dev,
+                               struct device_attribute *attr,
+                               char *buf)
+{
+       struct a21_wdt_drv *drv = dev_get_drvdata(dev);
+       unsigned int reset = 0;
+
+       if (!drv)
+               return -EIO;
+
+       reset = a21_wdt_get_bootstatus(drv);
+
+       return sprintf(buf, "%s\n", reset_causes[reset]);
+}
+static DEVICE_ATTR(rebootcause, S_IRUGO, rebootcause_show, NULL);

I actually need the check for if (!drv) to prevent an OOPS, as
dev_get_drvdata(dev) returns NULL., though it is set at the end of my probe
function via:

[...]
+       ret = watchdog_register_device(&a21_wdt);
+       if (ret) {
+               dev_err(&pdev->dev, "Cannot register watchdog device\n");
+               goto err_register_wd;
+       }
+
+       dev_set_drvdata(&pdev->dev, drv);
+
+       return 0;
[...]

The watchdog driver itself is working without any troubles.

Some advice here would be worth its weight in gold.

Thanks,
Johannes
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