linux-watchdog.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Robin Gong <yibin.gong@nxp.com>
To: Guenter Roeck <linux@roeck-us.net>,
	"wim@linux-watchdog.org" <wim@linux-watchdog.org>,
	"shawnguo@kernel.org" <shawnguo@kernel.org>,
	"s.hauer@pengutronix.de" <s.hauer@pengutronix.de>,
	"festevam@gmail.com" <festevam@gmail.com>
Cc: dl-linux-imx <linux-imx@nxp.com>,
	"kernel@pengutronix.de" <kernel@pengutronix.de>,
	"linux-watchdog@vger.kernel.org" <linux-watchdog@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v1] watchdog: imx2_wdt: clear WDOG_HW_RUNNING before suspend
Date: Wed, 12 May 2021 11:34:37 +0000	[thread overview]
Message-ID: <VE1PR04MB66889A576AD92D4D789199D489529@VE1PR04MB6688.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <d5364293-8cba-0d39-aa45-a55c5d6d2af6@roeck-us.net>

On 2021/05/11 11:59 Guenter Roeck <groeck7@gmail.com> wrote: 
> On 5/11/21 4:20 AM, Robin Gong wrote:
> > Since watchdog_ping_work is not freezable so that it maybe scheduled
> > before imx2_wdt_resume where watchdog clock enabled, hence, kernel
> > will hang in imx2_wdt_ping without clock, and then watchdog reset
> > happen. Prevent the above case by clearing WDOG_HW_RUNNING before
> > suspend, and restore it with ping in imx2_wdt_resume.
> >
> > Signed-off-by: Robin Gong <yibin.gong@nxp.com>
> > ---
> >   drivers/watchdog/imx2_wdt.c | 8 ++++++++
> >   1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/watchdog/imx2_wdt.c b/drivers/watchdog/imx2_wdt.c
> > index b84f80f..d3751e9 100644
> > --- a/drivers/watchdog/imx2_wdt.c
> > +++ b/drivers/watchdog/imx2_wdt.c
> > @@ -357,6 +357,13 @@ static int __maybe_unused
> imx2_wdt_suspend(struct device *dev)
> >   		 */
> >   		__imx2_wdt_set_timeout(wdog, IMX2_WDT_MAX_TIME);
> >   		imx2_wdt_ping(wdog);
> > +
> > +		/*
> > +		 * clear WDOG_HW_RUNNING to prevent watchdog_ping_work
> running
> > +		 * before imx2_wdt_resume where clock enabled, otherwise kernel
> > +		 * will hang and watchdog reset happen then.
> > +		 */
> > +		clear_bit(WDOG_HW_RUNNING, &wdog->status);
> >   	}
> >
> >   	clk_disable_unprepare(wdev->clk);
> > @@ -386,6 +393,7 @@ static int __maybe_unused imx2_wdt_resume(struct
> device *dev)
> >   	if (imx2_wdt_is_running(wdev)) {
> >   		imx2_wdt_set_timeout(wdog, wdog->timeout);
> >   		imx2_wdt_ping(wdog);
> > +		set_bit(WDOG_HW_RUNNING, &wdog->status);
> >   	}
> >
> >   	return 0;
> >
> I really don't like this; it depends on assumptions how the watchdog core
> works, and it misuses WDOG_HW_RUNNING to indicate that the clock is
> stopped (or that the driver is in suspend mode).
> 
> If ping doesn't work with the clock stopped, I think it would be much better to
> have a flag indicating that the clock is stopped, and have the ping function do
> nothing if it is called with stopped clock (ie if suspended).
> 
Understood, but I think that corner case should be a common potential issue
in all watchdog drivers which disable clock in suspend with WDOG_HW_RUNNING.
So common way looks better than many different specific flags in such different
watchdog driver with the similar intention?

BTW, for i.mx2_wdt which watchdog can't be stop unless kernel enter into suspend,
that seems like watchdog stop after suspend and clear WDOG_HW_RUNNING makes
sense? 


  reply	other threads:[~2021-05-12 11:34 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-11 11:20 Robin Gong
2021-05-11  3:59 ` Guenter Roeck
2021-05-12 11:34   ` Robin Gong [this message]
2021-05-12 14:14     ` Guenter Roeck
2021-05-13  3:49       ` Robin Gong

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=VE1PR04MB66889A576AD92D4D789199D489529@VE1PR04MB6688.eurprd04.prod.outlook.com \
    --to=yibin.gong@nxp.com \
    --cc=festevam@gmail.com \
    --cc=kernel@pengutronix.de \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-imx@nxp.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-watchdog@vger.kernel.org \
    --cc=linux@roeck-us.net \
    --cc=s.hauer@pengutronix.de \
    --cc=shawnguo@kernel.org \
    --cc=wim@linux-watchdog.org \
    --subject='RE: [PATCH v1] watchdog: imx2_wdt: clear WDOG_HW_RUNNING before suspend' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).