Re: [PATCH 2/2] watchdog: rti: tweak min_hw_heartbeat_ms to match initial allowed window

[Jan Kiszka]

On 25.06.20 10:32, Tero Kristo wrote:
> On 24/06/2020 18:24, Jan Kiszka wrote:
> > On 24.06.20 13:45, Tero Kristo wrote:
> > > If the RTI watchdog has been started by someone (like bootloader) when
> > > the driver probes, we must adjust the initial ping timeout to match the
> > > currently running watchdog window to avoid generating watchdog reset.
> > >
> > > Signed-off-by: Tero Kristo <t-kristo@xxxxxx>
> > > ---
> > > Â drivers/watchdog/rti_wdt.c | 25 +++++++++++++++++++++++++
> > > Â 1 file changed, 25 insertions(+)
> > >
> > > diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
> > > index d456dd72d99a..02ea2b2435f5 100644
> > > --- a/drivers/watchdog/rti_wdt.c
> > > +++ b/drivers/watchdog/rti_wdt.c
> > > @@ -55,11 +55,13 @@ static int heartbeat;
> > > ÂÂ * @base - base io address of WD device
> > > ÂÂ * @freq - source clock frequency of WDT
> > >  * @wdd - hold watchdog device as is in WDT core
> > > + * @min_hw_heartbeat_save - save of the min hw heartbeat value
> > > ÂÂ */
> > > Â struct rti_wdt_device {
> > > ÂÂÂÂÂ void __iomemÂÂÂÂÂÂÂ *base;
> > > ÂÂÂÂÂ unsigned longÂÂÂÂÂÂÂ freq;
> > > ÂÂÂÂÂ struct watchdog_deviceÂÂÂ wdd;
> > > +ÂÂÂ unsigned intÂÂÂÂÂÂÂ min_hw_heartbeat_save;
> > > Â };
> > > Â static int rti_wdt_start(struct watchdog_device *wdd)
> > > @@ -107,6 +109,11 @@ static int rti_wdt_ping(struct watchdog_device 
> > > *wdd)
> > > ÂÂÂÂÂ /* put watchdog in active state */
> > > ÂÂÂÂÂ writel_relaxed(WDKEY_SEQ1, wdt->base + RTIWDKEY);
> > > +ÂÂÂ if (wdt->min_hw_heartbeat_save) {
> > > +ÂÂÂÂÂÂÂ wdd->min_hw_heartbeat_ms = wdt->min_hw_heartbeat_save;
> > > +ÂÂÂÂÂÂÂ wdt->min_hw_heartbeat_save = 0;
> > > +ÂÂÂ }
> > > +
> > > ÂÂÂÂÂ return 0;
> > > Â }
> > > @@ -201,6 +208,24 @@ static int rti_wdt_probe(struct platform_device 
> > > *pdev)
> > > ÂÂÂÂÂÂÂÂÂ goto err_iomap;
> > > ÂÂÂÂÂ }
> > > +ÂÂÂ if (readl(wdt->base + RTIDWDCTRL) == WDENABLE_KEY) {
> > > +ÂÂÂÂÂÂÂ u32 time_left;
> > > +ÂÂÂÂÂÂÂ u32 heartbeat;
> > > +
> > > +ÂÂÂÂÂÂÂ set_bit(WDOG_HW_RUNNING, &wdd->status);
> > > +ÂÂÂÂÂÂÂ time_left = rti_wdt_get_timeleft(wdd);
> > > +ÂÂÂÂÂÂÂ heartbeat = readl(wdt->base + RTIDWDPRLD);
> > > +ÂÂÂÂÂÂÂ heartbeat <<= WDT_PRELOAD_SHIFT;
> > > +ÂÂÂÂÂÂÂ heartbeat /= wdt->freq;
> > > +ÂÂÂÂÂÂÂ if (time_left < heartbeat / 2)
> > > +ÂÂÂÂÂÂÂÂÂÂÂ wdd->min_hw_heartbeat_ms = 0;
> > > +ÂÂÂÂÂÂÂ else
> > > +ÂÂÂÂÂÂÂÂÂÂÂ wdd->min_hw_heartbeat_ms =
> > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ (time_left - heartbeat / 2 + 1) * 1000;
> > > +
> > > +ÂÂÂÂÂÂÂ wdt->min_hw_heartbeat_save = 11 * heartbeat * 1000 / 20;
> > > +ÂÂÂ }
> > > +
> > > ÂÂÂÂÂ ret = watchdog_register_device(wdd);
> > > ÂÂÂÂÂ if (ret) {
> > > ÂÂÂÂÂÂÂÂÂ dev_err(dev, "cannot register watchdog device\n");
> >
> > This assumes that the bootloader also programmed a 50% window, right? 
> > The pending U-Boot patch will do that, but what if that may chance or 
> > someone uses a different setup?
>
> Yes, we assume 50%. I think based on the hw design, 50% is the only sane 
> value to be used, otherwise you just shrink the open window too much and 
> for no apparent reason.

Fine with me, but should we check that assumption when adopting the 
watchdog?

Jan

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