Re: [PATCH v4 5/7] Watchdog: introduce ARM SBSA watchdog driver

[Guenter Roeck]

On 06/08/2015 09:05 AM, Fu Wei wrote:
> Hi Gurnter
>
> On 3 June 2015 at 01:07, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > On 06/02/2015 09:55 AM, Fu Wei wrote:
> > > Hi Timur,
> > >
> > > Thanks , feedback inline
> > >
> > > On 2 June 2015 at 23:32, Timur Tabi <timur@xxxxxxxxxxxxxx> wrote:
> > > > On 06/01/2015 11:05 PM, fu.wei@xxxxxxxxxx wrote:
> > > >
> > > > > +/*
> > > > > + * help functions for accessing 32bit registers of SBSA Generic
> > > > > Watchdog
> > > > > + */
> > > > > +static void sbsa_gwdt_cf_write(unsigned int reg, u32 val,
> > > > > +                              struct watchdog_device *wdd)
> > > > > +{
> > > > > +       struct sbsa_gwdt *gwdt = to_sbsa_gwdt(wdd);
> > > > > +
> > > > > +       writel_relaxed(val, gwdt->control_base + reg);
> > > > > +}
> > > > > +
> > > > > +static void sbsa_gwdt_rf_write(unsigned int reg, u32 val,
> > > > > +                              struct watchdog_device *wdd)
> > > > > +{
> > > > > +       struct sbsa_gwdt *gwdt = to_sbsa_gwdt(wdd);
> > > > > +
> > > > > +       writel_relaxed(val, gwdt->refresh_base + reg);
> > > > > +}
> > > > > +
> > > > > +static u32 sbsa_gwdt_cf_read(unsigned int reg, struct watchdog_device
> > > > > *wdd)
> > > > > +{
> > > > > +       struct sbsa_gwdt *gwdt = to_sbsa_gwdt(wdd);
> > > > > +
> > > > > +       return readl_relaxed(gwdt->control_base + reg);
> > > > > +}
> > > >
> > > >
> > > >
> > > > I still think you should get rid of these functions and just call
> > > > readl_relaxed() and writel_relaxed() every time, but I won't complain
> > > > again
> > > > if you keep them.
> > >
> > >
> > > yes, that make sense, and will reduce the size of code, and I think
> > > the code's readability will be OK too.
> > > will try in my next patch,
> > >
> > > > > +static irqreturn_t sbsa_gwdt_interrupt(int irq, void *dev_id)
> > > > > +{
> > > > > +       struct sbsa_gwdt *gwdt = (struct sbsa_gwdt *)dev_id;
> > > > > +       struct watchdog_device *wdd = &gwdt->wdd;
> > > > > +
> > > > > +       if (wdd->pretimeout)
> > > > > +               /* The pretimeout is valid, go panic */
> > > > > +               panic("SBSA Watchdog pre-timeout");
> > > > > +       else
> > > > > +               /* We don't use pretimeout, trigger WS1 now*/
> > > > > +               sbsa_gwdt_set_wcv(wdd, 0);
> > > >
> > > >
> > > >
> > > > I don't like this.
> > >
> > >
> > > If so, what is your idea ,if pretimeout == 0?
> > >
> > > the reason of using WCV as (timout - pretimeout): it can provide the
> > > longer timeout period,
> > > (1)If we use WOR, it can only provide 10s @ 400MHz(max).
> > > as Guenter said earlier, the default timer out for most watchdog will
> > > be 30s, so I think 10s limit will be a little short
> > > (2)we can always program WCV just like ping.
> > > (3)if a timeout arrives, WOR will be use, so use it as pretimeout, but
> > > we still can make this pretimeout longer by programming WCV(I don't
> > > think it's necessary)
> > >
> > >
> > > > The triggering of the hardware reset should never depend
> > > > on an interrupt being handled properly.
> > >
> > >
> > > if this fail, system reset in 1S, because WOR == (1s)
> > So ?
>
> Even the interrupt routine isn't triggered,  (WOR + system counter) --> WCV,
> then, sy system reset in 1S.
>
> the hardware reset doesn't depend on an interrupt.
>
>
> > > > You should always program WCV
> > > > correctly in advance.  This is especially true since pre-timeout will
> > > > probably rarely be used.
> > >
> > >
> > > always programming WCV is doable.  But I absolutely can not agree "
> > > pre-timeout will probably rarely be used"
> > > If so, SBSA watchdog is just a normal watchdog,  This use case just
> > > makes this HW useless.
> > > If so, go to use SP805.
> > > you still don't see the importance of this warning and pretimeout to a
> > > real server.
> >
> > If pretimeout isn't used, why not just set WCV = timeout, WOR = 0 ?
>
> Because if WOR = 0 , according to SBSA,  once you want to enable watchdog,
> (0 + system counter) --> WCV , then , WS0 and WS1 will be triggered immediately.
> we have not a chance(a time slot) to update WCV.

I would have thought that this is exactly what we want if pretimeout is not used.
What am I missing here ?

Guenter

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