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

[Tero Kristo]

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.

-Tero
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