hw/arm/nrf51: Wire up sysclk

Wire up the sysclk input to the armv7m object.

Strictly this SoC should not have a systick device at all, but our
armv7m container object doesn't currently support disabling the
systick device.  For the moment, add a TODO comment, but note that
this is why we aren't wiring up a refclk (no need for one).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alexandre Iooss <erdnaxe@crans.org>
Message-id: 20210812093356.1946-16-peter.maydell@linaro.org

hw/arm/nrf51_soc.c

@@ -12,6 +12,7 @@
 #include "qapi/error.h"
 #include "hw/arm/boot.h"
 #include "hw/sysbus.h"
+#include "hw/qdev-clock.h"
 #include "hw/misc/unimp.h"
 #include "qemu/log.h"
 
@@ -66,6 +67,23 @@ static void nrf51_soc_realize(DeviceState *dev_soc, Error **errp)
         return;
     }
 
+    /*
+     * HCLK on this SoC is fixed, so we set up sysclk ourselves and
+     * the board shouldn't connect it.
+     */
+    if (clock_has_source(s->sysclk)) {
+        error_setg(errp, "sysclk clock must not be wired up by the board code");
+        return;
+    }
+    /* This clock doesn't need migration because it is fixed-frequency */
+    clock_set_hz(s->sysclk, HCLK_FRQ);
+    qdev_connect_clock_in(DEVICE(&s->cpu), "cpuclk", s->sysclk);
+    /*
+     * This SoC has no systick device, so don't connect refclk.
+     * TODO: model the lack of systick (currently the armv7m object
+     * will always provide one).
+     */
+
     system_clock_scale = NANOSECONDS_PER_SECOND / HCLK_FRQ;
 
     object_property_set_link(OBJECT(&s->cpu), "memory", OBJECT(&s->container),
@@ -191,6 +209,8 @@ static void nrf51_soc_init(Object *obj)
                                 TYPE_NRF51_TIMER);
 
     }
+
+    s->sysclk = qdev_init_clock_in(DEVICE(s), "sysclk", NULL, NULL, 0);
 }
 
 static Property nrf51_soc_properties[] = {

include/hw/arm/nrf51_soc.h

@@ -17,6 +17,7 @@
 #include "hw/gpio/nrf51_gpio.h"
 #include "hw/nvram/nrf51_nvm.h"
 #include "hw/timer/nrf51_timer.h"
+#include "hw/clock.h"
 #include "qom/object.h"
 
 #define TYPE_NRF51_SOC "nrf51-soc"
@@ -50,6 +51,7 @@ struct NRF51State {
 
     MemoryRegion container;
 
+    Clock *sysclk;
 };
 
 #endif