hw/watchdog/sbsa_gwdt: Make watchdog timer frequency a QOM property

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.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20240426122913.3427983-4-peter.maydell@linaro.org

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);
     sysbus_realize_and_unref(s, &error_fatal);
     sysbus_mmio_map(s, 0, rbase);
     sysbus_mmio_map(s, 1, cbase);

hw/watchdog/sbsa_gwdt.c

@@ -18,6 +18,7 @@
 #include "qemu/osdep.h"
 #include "sysemu/reset.h"
 #include "sysemu/watchdog.h"
+#include "hw/qdev-properties.h"
 #include "hw/watchdog/sbsa_gwdt.h"
 #include "qemu/timer.h"
 #include "migration/vmstate.h"
@@ -109,7 +110,7 @@ static void sbsa_gwdt_update_timer(SBSA_GWDTState *s, WdtRefreshType rtype)
         timeout = s->woru;
         timeout <<= 32;
         timeout |= s->worl;
-        timeout = muldiv64(timeout, NANOSECONDS_PER_SECOND, SBSA_TIMER_FREQ);
+        timeout = muldiv64(timeout, NANOSECONDS_PER_SECOND, s->freq);
         timeout += qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 
         if ((rtype == EXPLICIT_REFRESH) || ((rtype == TIMEOUT_REFRESH) &&
@@ -261,6 +262,17 @@ static void wdt_sbsa_gwdt_realize(DeviceState *dev, Error **errp)
                 dev);
 }
 
+static Property wdt_sbsa_gwdt_props[] = {
+    /*
+     * Timer frequency in Hz. This must match the frequency used by
+     * the CPU's generic timer. Default 62.5Hz matches QEMU's legacy
+     * CPU timer frequency default.
+     */
+    DEFINE_PROP_UINT64("clock-frequency", struct SBSA_GWDTState, freq,
+                       62500000),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
 static void wdt_sbsa_gwdt_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
@@ -271,6 +283,7 @@ static void wdt_sbsa_gwdt_class_init(ObjectClass *klass, void *data)
     set_bit(DEVICE_CATEGORY_WATCHDOG, dc->categories);
     dc->vmsd = &vmstate_sbsa_gwdt;
     dc->desc = "SBSA-compliant generic watchdog device";
+    device_class_set_props(dc, wdt_sbsa_gwdt_props);
 }
 
 static const TypeInfo wdt_sbsa_gwdt_info = {

include/hw/watchdog/sbsa_gwdt.h

@@ -55,8 +55,6 @@
 #define SBSA_GWDT_RMMIO_SIZE 0x1000
 #define SBSA_GWDT_CMMIO_SIZE 0x1000
 
-#define SBSA_TIMER_FREQ      62500000 /* Hz */
-
 typedef struct SBSA_GWDTState {
     /* <private> */
     SysBusDevice parent_obj;
@@ -67,6 +65,7 @@ typedef struct SBSA_GWDTState {
     qemu_irq irq;
 
     QEMUTimer *timer;
+    uint64_t freq;
 
     uint32_t id;
     uint32_t wcs;