linux-kernel - RE: [PATCH] watchdog: imx2

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Date:   Mon, 24 Feb 2020 11:44:22 +0000
From:   Anson Huang <anson.huang@....com>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
CC:     "wim@...ux-watchdog.org" <wim@...ux-watchdog.org>,
        "linux@...ck-us.net" <linux@...ck-us.net>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH] watchdog: imx2_wdt: Drop .remove callback

Hi, Uwe

> Subject: Re: [PATCH] watchdog: imx2_wdt: Drop .remove callback
> 
> On Mon, Feb 24, 2020 at 10:51:27AM +0800, Anson Huang wrote:
> > .remove callback implementation doesn' call clk_disable_unprepare()
> > which is buggy, actually, we can just use
> > devm_watchdog_register_device() and
> > devm_add_action_or_reset() to handle all necessary operations for
> > remove action, then .remove callback can be dropped.
> >
> > Signed-off-by: Anson Huang <Anson.Huang@....com>
> > ---
> >  drivers/watchdog/imx2_wdt.c | 37
> > ++++++++++---------------------------
> >  1 file changed, 10 insertions(+), 27 deletions(-)
> >
> > diff --git a/drivers/watchdog/imx2_wdt.c b/drivers/watchdog/imx2_wdt.c
> > index f8d58bf..1fe472f 100644
> > --- a/drivers/watchdog/imx2_wdt.c
> > +++ b/drivers/watchdog/imx2_wdt.c
> > @@ -244,6 +244,11 @@ static const struct regmap_config
> imx2_wdt_regmap_config = {
> >  	.max_register = 0x8,
> >  };
> >
> > +static void imx2_wdt_action(void *data) {
> > +	clk_disable_unprepare(data);
> 
> Does this have the effect of stopping the watchdog? Maybe we can have a
> more expressive function name here (imx2_wdt_stop_clk or similar)?

This action is ONLY called when probe failed or device is removed, and if watchdog
is running, the core driver will prevent it from being removed.

> 
> Is there some watchdog core policy that tells if the watchdog should be
> stopped on unload?

watchdog_stop_on_unregister() should be called in .probe function to make core
policy stop the watchdog before removing it, but I think this driver does NOT call
it, maybe I should add the API call, need Guenter to help confirm.

> 
> > +}
> > +
> >  static int __init imx2_wdt_probe(struct platform_device *pdev)  {
> >  	struct device *dev = &pdev->dev;
> > @@ -292,6 +297,10 @@ static int __init imx2_wdt_probe(struct
> platform_device *pdev)
> >  	if (ret)
> >  		return ret;
> >
> > +	ret = devm_add_action_or_reset(dev, imx2_wdt_action, wdev->clk);
> > +	if (ret)
> > +		return ret;
> > +
> >  	regmap_read(wdev->regmap, IMX2_WDT_WRSR, &val);
> >  	wdog->bootstatus = val & IMX2_WDT_WRSR_TOUT ?
> WDIOF_CARDRESET : 0;
> >
> > @@ -315,32 +324,7 @@ static int __init imx2_wdt_probe(struct
> platform_device *pdev)
> >  	 */
> >  	regmap_write(wdev->regmap, IMX2_WDT_WMCR, 0);
> >
> > -	ret = watchdog_register_device(wdog);
> > -	if (ret)
> > -		goto disable_clk;
> > -
> > -	dev_info(dev, "timeout %d sec (nowayout=%d)\n",
> > -		 wdog->timeout, nowayout);
> 
> Does the core put this info in the kernel log? If not dropping it isn't obviously
> right enough to be done en passant.

This is just an info for user which I think NOT unnecessary, so I drop it in this patch
as well.

> 
> > -	return 0;
> > -
> > -disable_clk:
> > -	clk_disable_unprepare(wdev->clk);
> > -	return ret;
> > -}
> > -
> > -static int __exit imx2_wdt_remove(struct platform_device *pdev) -{
> > -	struct watchdog_device *wdog = platform_get_drvdata(pdev);
> > -	struct imx2_wdt_device *wdev = watchdog_get_drvdata(wdog);
> > -
> > -	watchdog_unregister_device(wdog);
> > -
> > -	if (imx2_wdt_is_running(wdev)) {
> > -		imx2_wdt_ping(wdog);
> > -		dev_crit(&pdev->dev, "Device removed: Expect reboot!\n");
> > -	}
> 
> I also wonder about this one. This changes the timing behaviour and so
> IMHO shouldn't be done as a side effect of a cleanup patch.

Guenter has a comment of "use devm_watchdog_register_device(), and the watchdog subsystem
should prevent removal if the watchdog is running ", so I thought no need to check the watchdog's
status here, but after further check the core code of watchdog_cdev_unregister() function, I ONLY
see it will check whether need to stop watchdog before unregister,

...

1083         if (watchdog_active(wdd) &&
1084             test_bit(WDOG_STOP_ON_UNREGISTER, &wdd->status)) {
1085                 watchdog_stop(wdd);
1086         }

Hi, Guenter
	Do you think watchdog_stop_on_unregister() should be called in .probe function to
make watchdog stop before unregister?

Thanks,
Anson.