hw/arm/stm32f405: Wire up sysclk and refclk

Wire up the sysclk and refclk for the stm32f405 SoC.  This SoC always
runs the systick refclk at 1/8 the frequency of the main CPU clock,
so the board code only needs to provide a single sysclk clock.

Because there is only one board using this SoC, we convert the SoC
and the board together, rather than splitting it into "add clock to
SoC; connect clock in board; add error check in SoC code that clock
is wired up".

When the systick device starts honouring its clock inputs, this will
fix an emulation inaccuracy in the netduinoplus2 board where the
systick reference clock was running at 1MHz rather than 21MHz.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Alexandre Iooss <erdnaxe@crans.org>
Reviewed-by: Luc Michel <luc@lmichel.fr>
Message-id: 20210812093356.1946-14-peter.maydell@linaro.org

hw/arm/netduinoplus2.c

@@ -26,6 +26,7 @@
 #include "qapi/error.h"
 #include "hw/boards.h"
 #include "hw/qdev-properties.h"
+#include "hw/qdev-clock.h"
 #include "qemu/error-report.h"
 #include "hw/arm/stm32f405_soc.h"
 #include "hw/arm/boot.h"
@@ -36,16 +37,17 @@
 static void netduinoplus2_init(MachineState *machine)
 {
     DeviceState *dev;
+    Clock *sysclk;
 
-    /*
-     * TODO: ideally we would model the SoC RCC and let it handle
-     * system_clock_scale, including its ability to define different
-     * possible SYSCLK sources.
-     */
     system_clock_scale = NANOSECONDS_PER_SECOND / SYSCLK_FRQ;
 
+    /* This clock doesn't need migration because it is fixed-frequency */
+    sysclk = clock_new(OBJECT(machine), "SYSCLK");
+    clock_set_hz(sysclk, SYSCLK_FRQ);
+
     dev = qdev_new(TYPE_STM32F405_SOC);
     qdev_prop_set_string(dev, "cpu-type", ARM_CPU_TYPE_NAME("cortex-m4"));
+    qdev_connect_clock_in(dev, "sysclk", sysclk);
     sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), &error_fatal);
 
     armv7m_load_kernel(ARM_CPU(first_cpu),

hw/arm/stm32f405_soc.c

@@ -28,6 +28,7 @@
 #include "exec/address-spaces.h"
 #include "sysemu/sysemu.h"
 #include "hw/arm/stm32f405_soc.h"
+#include "hw/qdev-clock.h"
 #include "hw/misc/unimp.h"
 
 #define SYSCFG_ADD                     0x40013800
@@ -80,6 +81,9 @@ static void stm32f405_soc_initfn(Object *obj)
     }
 
     object_initialize_child(obj, "exti", &s->exti, TYPE_STM32F4XX_EXTI);
+
+    s->sysclk = qdev_init_clock_in(DEVICE(s), "sysclk", NULL, NULL, 0);
+    s->refclk = qdev_init_clock_in(DEVICE(s), "refclk", NULL, NULL, 0);
 }
 
 static void stm32f405_soc_realize(DeviceState *dev_soc, Error **errp)
@@ -91,6 +95,30 @@ static void stm32f405_soc_realize(DeviceState *dev_soc, Error **errp)
     Error *err = NULL;
     int i;
 
+    /*
+     * We use s->refclk internally and only define it with qdev_init_clock_in()
+     * so it is correctly parented and not leaked on an init/deinit; it is not
+     * intended as an externally exposed clock.
+     */
+    if (clock_has_source(s->refclk)) {
+        error_setg(errp, "refclk clock must not be wired up by the board code");
+        return;
+    }
+
+    if (!clock_has_source(s->sysclk)) {
+        error_setg(errp, "sysclk clock must be wired up by the board code");
+        return;
+    }
+
+    /*
+     * TODO: ideally we should model the SoC RCC and its ability to
+     * change the sysclk frequency and define different sysclk sources.
+     */
+
+    /* The refclk always runs at frequency HCLK / 8 */
+    clock_set_mul_div(s->refclk, 8, 1);
+    clock_set_source(s->refclk, s->sysclk);
+
     memory_region_init_rom(&s->flash, OBJECT(dev_soc), "STM32F405.flash",
                            FLASH_SIZE, &err);
     if (err != NULL) {
@@ -116,6 +144,8 @@ static void stm32f405_soc_realize(DeviceState *dev_soc, Error **errp)
     qdev_prop_set_uint32(armv7m, "num-irq", 96);
     qdev_prop_set_string(armv7m, "cpu-type", s->cpu_type);
     qdev_prop_set_bit(armv7m, "enable-bitband", true);
+    qdev_connect_clock_in(armv7m, "cpuclk", s->sysclk);
+    qdev_connect_clock_in(armv7m, "refclk", s->refclk);
     object_property_set_link(OBJECT(&s->armv7m), "memory",
                              OBJECT(system_memory), &error_abort);
     if (!sysbus_realize(SYS_BUS_DEVICE(&s->armv7m), errp)) {

include/hw/arm/stm32f405_soc.h

@@ -68,6 +68,9 @@ struct STM32F405State {
     MemoryRegion sram;
     MemoryRegion flash;
     MemoryRegion flash_alias;
+
+    Clock *sysclk;
+    Clock *refclk;
 };
 
 #endif