Re: [PATCH v2 10/21] arm: sbsa_gwdt: add 'wdat' option

[Igor Mammedov <imammedo@redhat.com>]

On Tue, 26 May 2026 16:24:59 +0200
Eric Auger <eauger@redhat.com> wrote:

> On 3/3/26 10:25 AM, Igor Mammedov wrote:
> > it will be used by arm/virt board, to pick WDAT compatible watchdog impl.
> > and act as switch over to WDAT ACPI table vesus default GTDT ACPI table.
> > 
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > ---
> >  include/hw/watchdog/sbsa_gwdt.h | 1 +
> >  hw/watchdog/sbsa_gwdt.c         | 8 ++++++++
> >  2 files changed, 9 insertions(+)
> > 
> > diff --git a/include/hw/watchdog/sbsa_gwdt.h b/include/hw/watchdog/sbsa_gwdt.h
> > index 307a4f291a..dc77e6be60 100644
> > --- a/include/hw/watchdog/sbsa_gwdt.h
> > +++ b/include/hw/watchdog/sbsa_gwdt.h
> > @@ -73,6 +73,7 @@ typedef struct SBSA_GWDTState {
> >      uint32_t woru;
> >      uint32_t wcvl;
> >      uint32_t wcvu;
> > +    bool wdat;
> >  } SBSA_GWDTState;
> >  
> >  #endif /* WDT_SBSA_GWDT_H */
> > diff --git a/hw/watchdog/sbsa_gwdt.c b/hw/watchdog/sbsa_gwdt.c
> > index c4dd8005b7..40d80f7f2b 100644
> > --- a/hw/watchdog/sbsa_gwdt.c
> > +++ b/hw/watchdog/sbsa_gwdt.c
> > @@ -265,6 +265,13 @@ static void wdt_sbsa_gwdt_realize(DeviceState *dev, Error **errp)
> >  
> >      sysbus_init_irq(sbd, &s->irq);
> >  
> > +    /*
> > +     * WDAT supports only upto 1KHz resolution,
> > +     */
> > +    if (s->wdat) {
> > +        s->freq = 1000;  
> where is it specified in the spec?

next patch has link to WDAT spec and
comment around relevant field:

+    /*
+     * WDAT spec suports only 1KHz or more coarse watchdog timer,
+     * Set resolution to minimum supported 1ms.
+     * Before starting watchdog Windows set countdown value to 5min.
+     */
+    g_assert(freq <= 1000);
+    build_append_int_noprefix(table_data, 1, 4);/* Timer Period, ms */

it's the hack to make gwdt usable for wdat and is applied only when
wdat is enabled, if not the gwdt is instantiated with native 1G and
provides corresponding fdt.

> 
> Thanks
> 
> Eric
> 
> > +    }
> > +
> >      s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, sbsa_gwdt_timer_sysinterrupt,
> >                  dev);
> >  }
> > @@ -276,6 +283,7 @@ static const Property wdt_sbsa_gwdt_props[] = {
> >       */
> >      DEFINE_PROP_UINT64("clock-frequency", struct SBSA_GWDTState, freq,
> >                         1000000000),
> > +    DEFINE_PROP_BOOL("wdat", struct SBSA_GWDTState, wdat, false),
> >  };
> >  
> >  static void wdt_sbsa_gwdt_class_init(ObjectClass *klass, const void *data)  
>