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

From: Anson Huang <anson.huang@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>,
	"kernel@pengutronix.de" <kernel@pengutronix.de>,
	"festevam@gmail.com" <festevam@gmail.com>,
	"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>
Cc: dl-linux-imx <linux-imx@nxp.com>
Subject: RE: [PATCH V2 1/2] watchdog: imx7ulp: Strictly follow the sequence for wdog operations
Date: Wed, 29 Jul 2020 04:50:06 +0000	[thread overview]
Message-ID: <DB3PR0402MB3916C412DE1E83A2D40B2341F5700@DB3PR0402MB3916.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <00587a78-8069-4fbd-7e02-b774d541f75a@roeck-us.net>

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@nxp.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