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

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Date:   Wed, 29 Jul 2020 04:50:06 +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
> 
> 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.

> 
> Also, I do not believe that a 10 milli-second timeout is warranted.
> This will need to be backed up by the datasheet.
> 

There is no such info provided in reference manual or datasheet, but I just did
an experiment, the unlock window is open in less than 1us after sending unlock command,
and ONLY last for ONLY 2~3 us then close, the reconfiguration status bit will be set in less than
1us after register write. So what do you recommend for this timeout value? 100mS for safe?

Thanks,
Anson