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

[Anson Huang <anson.huang@nxp.com>]

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));
> > +}
> > +
> >  static void imx7ulp_wdt_enable(struct watchdog_device *wdog, bool
> > enable)  {
> >  	struct imx7ulp_wdt_device *wdt = watchdog_get_drvdata(wdog);
> >
> >  	u32 val = readl(wdt->base + WDOG_CS);
> >
> > +	local_irq_disable();
> >  	writel(UNLOCK, wdt->base + WDOG_CNT);
> > +	imx7ulp_wdt_wait(wdt->base, WDOG_CS_ULK);
> >  	if (enable)
> >  		writel(val | WDOG_CS_EN, wdt->base + WDOG_CS);
> >  	else
> >  		writel(val & ~WDOG_CS_EN, wdt->base + WDOG_CS);
> > +	imx7ulp_wdt_wait(wdt->base, WDOG_CS_RCS);
> > +	local_irq_enable();
> >  }
> >
> >  static bool imx7ulp_wdt_is_enabled(void __iomem *base) @@ -72,7
> > +88,12 @@ static int imx7ulp_wdt_ping(struct watchdog_device *wdog)  {
> >  	struct imx7ulp_wdt_device *wdt = watchdog_get_drvdata(wdog);
> >
> > +	local_irq_disable();
> > +	writel(UNLOCK, wdt->base + WDOG_CNT);
> > +	imx7ulp_wdt_wait(wdt->base, WDOG_CS_ULK);
> >  	writel(REFRESH, wdt->base + WDOG_CNT);
> > +	imx7ulp_wdt_wait(wdt->base, WDOG_CS_RCS);
> 
> Per reference manual (section 59.5.4), the waits are not required here, and
> neither is the unlock. For practical purposes, disabling interrupts is useless as
> well since the refresh write operation is just a single register write.

Correct, the example in reference manual does NOT have this flow for refresh, but
I checked with our design team yestoday, their validation code indeed has this flow,
that is why I added it for refresh operation as well.
I will do a test on our EVK board, and if it works without this flow, I will remove them
In V3.

Thanks,
Anson