linux-kernel - Re: [PATCH v2 06/11] watchdog/hpwdt: Modify to use watchdog core.

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Date:   Tue, 13 Feb 2018 13:55:49 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Jerry Hoemann <jerry.hoemann@....com>
Cc:     Marcus Folkesson <marcus.folkesson@...il.com>,
        wim@...ux-watchdog.org, linux-watchdog@...r.kernel.org,
        linux-kernel@...r.kernel.org, rwright@....com,
        maurice.a.saldivar@....com
Subject: Re: [PATCH v2 06/11] watchdog/hpwdt: Modify to use watchdog core.

On Tue, Feb 13, 2018 at 02:36:48PM -0700, Jerry Hoemann wrote:
> 
> 
> Thanks for the review. Comments inline.
> 
> On Mon, Feb 12, 2018 at 10:06:21AM +0100, Marcus Folkesson wrote:
> > Hi Jerry,
> > 
> > On Sun, Feb 11, 2018 at 10:21:06PM -0700, Jerry Hoemann wrote:
> > > Follow Documentation/watchdog/convert_drivers_to_kernel_api.txt to
> > > convert hpwdt from legacy watchdog driver to use the watchdog core.
> > > 
> > > Removed functions: hpwdt_open, hpwdt_release, hpwdt_write, hpwdt_ioctl
> > > Removed data structures: hpwdt_fops, hpwdt_miscdev, watchdog_device
> > > Modified functions: hpwdt_start, hpwdt_stop, hpwdt_ping, hpwdt_gettimeleft
> > > Added functions: hpwdt_settimeout
> > > Added structures: watchdog_device
> > > 
> > > Signed-off-by: Jerry Hoemann <jerry.hoemann@....com>
> > 
> > I think it would be better to use
> >     dev_emerg()
> >     dev_crit()
> >     dev_alert()
> >     dev_err()
> >     dev_warn()
> >     dev_notice()
> > 
> > instead of pr_* functions now when we have a device to use.
> 
> In general, is there something bad with using pr_debug, etc.,?
> 

No, but it is desirable to use dev_ functions where possible.

> When converting the driver over, I had many more debug messages being
> printed from locations where I didn't have a valid device handle and
> those needed to be done w/ the pr_.* functions.  So, I just uniformally
> used pr_.*.
> 
> 
> > > -static int hpwdt_time_left(void)
> > > +static unsigned int hpwdt_gettimeleft(struct watchdog_device *dev)
> > >  {
> > >  	return TICKS_TO_SECS(ioread16(hpwdt_timer_reg));
> > >  }
> > >  
> > > +static int hpwdt_settimeout(struct watchdog_device *dev, unsigned int val)
> > > +{
> > > +	pr_debug("settimeout = %d\n", val);
> > 
> > dev_dbg()
> 
> I think you are proposing I do:
> 
> 	dev_dbg(dev->parent, "settimeout = %d\n", val);
> 
> This raises the issue that I didn't set parent and I believe I should have.
> 
Correct.

> 
> > 
> > 
> > > +
> > > +	soft_margin = dev->timeout = val;
> > 
> > No need to update soft_margin
> 
> I'd made the permission on the module parameters 0444 so that they
> would show up in sysfs.  I updated this value so that I could see
> current value of timeout in sysfs.  But, as Guenter points out in a
> later review, these values are available in under CONFIG_WATCHDOG_SYSFS.
> So, I'll remove.
> 
> 
> > > +	pr_debug("nmi: ulReason=%d, mynmi=0x%0x\n", ulReason, mynmi);
> > 
> > dev_dbg()
> 
> See above.
> 
> > 
> > >  	retval = hpwdt_init_nmi_decoding(dev);
> > >  	if (retval != 0)
> > >  		goto error_init_nmi_decoding;
> > >  
> > > -	retval = misc_register(&hpwdt_miscdev);
> > > +	retval = watchdog_register_device(&hpwdt_dev);
> > >  	if (retval < 0) {
> > > -		dev_warn(&dev->dev,
> > > -			"Unable to register miscdev on minor=%d (err=%d).\n",
> > > -			WATCHDOG_MINOR, retval);
> > > -		goto error_misc_register;
> > > +		dev_warn(&dev->dev, "Unable to register hpe watchdog (err=%d).\n", retval);
> > > +		goto error_wd_register;
> > > +	}
> > > +
> > > +	watchdog_set_nowayout(&hpwdt_dev, nowayout);
> > > +	if (watchdog_init_timeout(&hpwdt_dev, soft_margin, NULL)) {
> > > +		dev_warn(&dev->dev, "Invalid soft_margin: %d. Using default\n", soft_margin);
> > > +		soft_margin = DEFAULT_MARGIN;
> > >  	}
> > 
> > In this case watchdog_init_timout() will:
> > 1) Check if soft_margin is valid
> > 2) if not, keep hpwdt_dev.timout intact (which is already set in
> > declaration of hpwdt_dev)
> > 
> > So we could remove the condition and only keep
> > watchdog_init_timeout(&hpwdt_dev, soft_margin, NULL);
> > 
> > 
> > Also, we need to set an invalid initial value for soft_margin to make
> > the logic for watchdog_init_timeout work. 
> > 
> > i.e
> > - static unsigned int soft_margin = DEFAULT_MARGIN;	/* in seconds */
> > + static unsigned int soft_margin;
> 
> 
> I don't see the core printing a warning message if an invalid value
> is specified for soft_margin when loading the module.
> 
> I don't mind the hpwdt module correcting an out of range parameter, but I
> don't think it should do so siliently.
> 

The point here is that setting soft_margin to 0 and setting the
timeout in the watchdog_device structure to DEFAULT_MARGIN
means that it is not necessary to override it on error.
If you want to be verbose, you can still log a warning message
if the timeout provided by the module parameter is wrong.

Anyway, this driver will presumably never support devicetree,
so the watchdog core will never read the timeout from there,
and this is not a showstopper.

Guenter