Re: [PATCH 1/1] gpio_wdt: change initcall level

[Jean-Baptiste Theou]

Hi Guenter,

I based my work on the work done in mpc8xxx_wdt.c, which is in mainline.

The point of my patch is for a built-in scenario.
I have an external chip who controls the watchdog, and it need to have 
it IN pin toggle within 1.6s, otherwise it trigger the watchdog.

With a default gpio_wdt built-in module, module_init initcall level is 
too late, and the board reboot (the watchdog cannot be disabled, I am 
using "always-running" property of this module.)

The point of my patch is to start the watchdog at arch_init call level,
and the "tweak" for late init is due to the fact that miscdev is not 
ready at the level of initcall, as explained on the comment.

If there is some part that aren't clear and if you have a better idea 
on how to raise the level of initcall for this module, on a cleaner 
way, I am all hears.

Best regards,

On Thu, 4 Jun 2015 21:37:03 -0700
Guenter Roeck <linux@xxxxxxxxxxxx> wrote:

> On 06/04/2015 12:21 PM, Jean-Baptiste Theou wrote:
> > gpio_wdt may need to start the GPIO toggle as soon as possible,
> > when the watchdog cannot be disabled. Raise the initcall to
> > arch_initcall.
> >
> > We need to split the initiation, because of miscdev, as done in
> > mpc8xxx_wdt.c
> >
> > Signed-off-by: Jean-Baptiste Theou <jtheou@xxxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/watchdog/gpio_wdt.c | 78 ++++++++++++++++++++++++++++++++++++++++++---
> >   1 file changed, 74 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/watchdog/gpio_wdt.c b/drivers/watchdog/gpio_wdt.c
> > index cbc313d..8ecfe7e 100644
> > --- a/drivers/watchdog/gpio_wdt.c
> > +++ b/drivers/watchdog/gpio_wdt.c
> > @@ -14,6 +14,7 @@
> >   #include <linux/module.h>
> >   #include <linux/notifier.h>
> >   #include <linux/of_gpio.h>
> > +#include <linux/of_platform.h>
> >   #include <linux/platform_device.h>
> >   #include <linux/reboot.h>
> >   #include <linux/watchdog.h>
> > @@ -223,10 +224,11 @@ static int gpio_wdt_probe(struct platform_device *pdev)
> >
> >   	setup_timer(&priv->timer, gpio_wdt_hwping, (unsigned long)&priv->wdd);
> >
> > -	ret = watchdog_register_device(&priv->wdd);
> > +#ifdef MODULE
> > +	ret = gpio_wdt_init_late();
> >   	if (ret)
> >   		return ret;
> > -
> > +#endif
> >   	priv->notifier.notifier_call = gpio_wdt_notify_sys;
> >   	ret = register_reboot_notifier(&priv->notifier);
> >   	if (ret)
> > @@ -235,10 +237,13 @@ static int gpio_wdt_probe(struct platform_device *pdev)
> >   	if (priv->always_running)
> >   		gpio_wdt_start_impl(priv);
> >
> > +	platform_set_drvdata(pdev, priv);
> >   	return 0;
> >
> >   error_unregister:
> > -	watchdog_unregister_device(&priv->wdd);
> > +#ifdef MODULE
> > +	ret = gpio_wdt_remove_late(&priv->wdd);
> > +#endif
> >   	return ret;
> >   }
> >
> > @@ -267,7 +272,72 @@ static struct platform_driver gpio_wdt_driver = {
> >   	.probe	= gpio_wdt_probe,
> >   	.remove	= gpio_wdt_remove,
> >   };
> > -module_platform_driver(gpio_wdt_driver);
> > +
> > +/*
> > + * We do wdt initialization in two steps: arch_initcall probes the wdt
> > + * very early to start pinging the watchdog (misc devices are not yet
> > + * available), and later module_init() just registers the misc device.
> > + */
> > +static int gpio_wdt_init_late(void)
> > +{
> > +	struct platform_device *pdev;
> > +	struct device_node *wdt_node;
> > +	struct gpio_wdt_priv *priv;
> > +	int ret;
> > +
> > +	for_each_compatible_node(wdt_node, NULL, "linux,wdt-gpio") {
> > +		pdev = of_find_device_by_node(wdt_node);
> > +		priv = platform_get_drvdata(pdev);
> > +		if (&priv->wdd) {
> > +			ret = watchdog_register_device(&priv->wdd);
> > +			if (ret)
> > +				return ret;
> > +		} else {
> > +			dev_err(&pdev->dev, "Unable to register the watchdog\n");
> > +			return -1;
> > +		}
> > +	}
> > +	return 0;
> > +}
> > +#ifndef MODULE
> > +module_init(gpio_wdt_init_late);
> > +#endif
> > +
> > +#ifdef MODULE
> > +int gpio_wdt_remove_late(void)
> > +{
> > +	struct platform_device *pdev;
> > +	struct device_node *wdt_node;
> > +	struct gpio_wdt_priv *priv;
> > +	int ret;
> > +
> > +	for_each_compatible_node(wdt_node, NULL, "linux,wdt-gpio") {
> > +		pdev = of_find_device_by_node(wdt_node);
> > +		priv = platform_get_drvdata(pdev);
> > +		if (&priv->wdd) {
> > +			ret = watchdog_unregister_device(&priv->wdd);
> > +			if (ret)
> > +				return ret;
> > +		} else {
> > +			dev_err(&pdev->dev, "Unable to register the watchdog\n");
> > +			return -1;
> > +		}
> > +	}
> > +	return 0;
> > +}
> > +#endif
> > +
> > +static int __init gpio_wdt_init(void)
> > +{
> > +	return platform_driver_register(&gpio_wdt_driver);
> > +}
> > +arch_initcall(gpio_wdt_init);
> > +
> > +static void __exit gpio_wdt_exit(void)
> > +{
> > +	platform_driver_unregister(&gpio_wdt_driver);
> > +}
> > +module_exit(gpio_wdt_exit);
> >
> >   MODULE_AUTHOR("Alexander Shiyan <shc_work@xxxxxxx>");
> >   MODULE_DESCRIPTION("GPIO Watchdog");
> >
> 
> This looks really messy, you don't explain why you think you need
> gpio_wdt_remove_late, and I do wonder if there are compile warnings
> when this is compiled as module.
> 
> If, in a given system, initialization can not wait until modules are loaded,
> maybe it makes more sense to build the driver into the kernel instead of
> introducing all this mess. If built into the kernel the latency should
> not be that bad that this is really needed.
> 
> Guenter
> 


-- 
Jean-Baptiste Theou <jtheou@xxxxxxxxxxxxxxxxx>
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