On Fri, 26 Apr 2024 at 13:46, Philippe Mathieu-Daudé <phi...@linaro.org> wrote: > > Hi Peter, > > On 26/4/24 14:29, Peter Maydell wrote: > > Currently the sbsa_gdwt watchdog device hardcodes its frequency at > > 62.5MHz. In real hardware, this watchdog is supposed to be driven > > from the system counter, which also drives the CPU generic timers. > > Newer CPU types (in particular from Armv8.6) should have a CPU > > generic timer frequency of 1GHz, so we can't leave the watchdog > > on the old QEMU default of 62.5GHz. > > > > Make the frequency a QOM property so it can be set by the board, > > and have our only board that uses this device set that frequency > > to the same value it sets the CPU frequency. > > > > Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> > > --- > > include/hw/watchdog/sbsa_gwdt.h | 3 +-- > > hw/arm/sbsa-ref.c | 1 + > > hw/watchdog/sbsa_gwdt.c | 15 ++++++++++++++- > > 3 files changed, 16 insertions(+), 3 deletions(-) > > > > diff --git a/hw/arm/sbsa-ref.c b/hw/arm/sbsa-ref.c > > index 36f6f717b4b..57c337fd92a 100644 > > --- a/hw/arm/sbsa-ref.c > > +++ b/hw/arm/sbsa-ref.c > > @@ -543,6 +543,7 @@ static void create_wdt(const SBSAMachineState *sms) > > SysBusDevice *s = SYS_BUS_DEVICE(dev); > > int irq = sbsa_ref_irqmap[SBSA_GWDT_WS0]; > > > > + qdev_prop_set_uint64(dev, "clock-frequency", SBSA_GTIMER_HZ); > > Since we have access to the CPU and its generic timer, what about > just keep the wdg in sync, as smth like: > > qdev_prop_set_uint64(dev, "clock-frequency", > object_property_get_uint(OBJECT(some_cpu), > "cntfrq", errp));
That introduces an implicit ordering requirement that the CPU has been created before the watchdog, which I'm not super enthusiastic about. "The platform knows the frequency and sets it on the devices that care" seems more straightforward to me. (The really-follow-the-hardware approach here would be to model the memory mapped system counter and then wire that up to both the CPUs and the watchdog, but that's a lot of extra work. I have some half-baked patches in that direction but for the moment I figure doing the simple thing is all we need.) -- PMM
