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

[Tero Kristo]

On 25/06/2020 16:35, Guenter Roeck wrote:
> On 6/25/20 1:32 AM, 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.
>
> Not sure if that is a valid assumption. Someone who designs a watchdog
> with such a narrow ping window might as well also use it. The question
> is if you want to rely on that assumption, or check and change it if needed.

Right, if that is a blocker, I can modify the code. Should be maybe 
couple of lines addition.

> Also, I wonder if we should add an API function such as
> "set_last_hw_keepalive()" to avoid all that complexity.

I can try adding that also if it is desirable.

-Tero
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