linux-kernel - RE: [PATCH V2 1/2] watchdog: imx7ulp: Strictly follow the sequence for wdog operations

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Message-ID: <DB3PR0402MB3916B38E7DA20A35403F5B1EF5700@DB3PR0402MB3916.eurprd04.prod.outlook.com>
Date:   Wed, 29 Jul 2020 05:02:33 +0000
From:   Anson Huang <anson.huang@....com>
To:     Guenter Roeck <linux@...ck-us.net>,
        "wim@...ux-watchdog.org" <wim@...ux-watchdog.org>,
        "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>
CC:     dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH V2 1/2] watchdog: imx7ulp: Strictly follow the sequence
 for wdog operations

Hi, Guenter


> Subject: RE: [PATCH V2 1/2] watchdog: imx7ulp: Strictly follow the sequence
> for wdog operations
> 
> Hi, Guenter
> 
> 
> > Subject: Re: [PATCH V2 1/2] watchdog: imx7ulp: Strictly follow the
> > sequence for wdog operations
> >
> > On 7/28/20 7:20 PM, Anson Huang wrote:
> > > According to reference manual, the i.MX7ULP WDOG's operations should
> > > follow below sequence:
> > >
> > > 1. disable global interrupts;
> > > 2. unlock the wdog and wait unlock bit set; 3. reconfigure the wdog
> > > and wait for reconfiguration bit set; 4. enabel global interrupts.
> > >
> > > Strictly follow the recommended sequence can make it more robust.
> > >
> > > Signed-off-by: Anson Huang <Anson.Huang@....com>
> > > ---
> > > Changes since V1:
> > > 	- use readl_poll_timeout_atomic() instead of usleep_ranges() since
> > > IRQ is
> > disabled.
> > > ---
> > >  drivers/watchdog/imx7ulp_wdt.c | 29 +++++++++++++++++++++++++++++
> > >  1 file changed, 29 insertions(+)
> > >
> > > diff --git a/drivers/watchdog/imx7ulp_wdt.c
> > > b/drivers/watchdog/imx7ulp_wdt.c index 7993c8c..7d2b12e 100644
> > > --- a/drivers/watchdog/imx7ulp_wdt.c
> > > +++ b/drivers/watchdog/imx7ulp_wdt.c
> > > @@ -5,6 +5,7 @@
> > >
> > >  #include <linux/clk.h>
> > >  #include <linux/io.h>
> > > +#include <linux/iopoll.h>
> > >  #include <linux/kernel.h>
> > >  #include <linux/module.h>
> > >  #include <linux/of.h>
> > > @@ -36,6 +37,7 @@
> > >  #define DEFAULT_TIMEOUT	60
> > >  #define MAX_TIMEOUT	128
> > >  #define WDOG_CLOCK_RATE	1000
> > > +#define WDOG_WAIT_TIMEOUT	10000
> > >
> > >  static bool nowayout = WATCHDOG_NOWAYOUT;
> > module_param(nowayout,
> > > bool, 0000); @@ -48,17 +50,31 @@ struct imx7ulp_wdt_device {
> > >  	struct clk *clk;
> > >  };
> > >
> > > +static inline void imx7ulp_wdt_wait(void __iomem *base, u32 mask) {
> > > +	u32 val = readl(base + WDOG_CS);
> > > +
> > > +	if (!(val & mask))
> > > +		WARN_ON(readl_poll_timeout_atomic(base + WDOG_CS, val,
> > > +						  val & mask, 0,
> > > +						  WDOG_WAIT_TIMEOUT));
> >
> > I am not a friend of WARN_ON, especially in situations like this.
> > Please explain why this is needed, and why a return of -ETIMEDOUT is
> > not feasible.
> 
> OK, I will use return value of -ETIMEOUT and handle it in the caller.

After a further look, some of the imx7ulp_wdt_wait () callers are void function, so if want
to handle the return value, all those functions return type need to be changed. And, when
the return value is -ETIMEDOUT, the ONLY action is to print out some error message
for these void function, need to use pr_err() due to no dev pointer available, so
do you think it is acceptable to just replace the WARN_ON with pr_err() as below?

+	if (!(val & mask)) {
+		if (readl_poll_timeout_atomic(base + WDOG_CS, val,
+						  val & mask, 0,
+						  WDOG_WAIT_TIMEOUT))
+           pr_err("wdog wait timeout, mask 0x%x\n", mask);
+   }

Thanks,
Anson