hpet: switch to fine-grained device locking

as a step towards lock-less HPET counter read,
use per device locking instead of BQL.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/20250814160600.2327672-4-imammedo@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/timer/hpet.c

@@ -38,6 +38,7 @@
 #include "hw/timer/i8254.h"
 #include "system/address-spaces.h"
 #include "qom/object.h"
+#include "qemu/lockable.h"
 #include "trace.h"
 
 struct hpet_fw_config hpet_fw_cfg = {.count = UINT8_MAX};
@@ -69,6 +70,7 @@ struct HPETState {
     SysBusDevice parent_obj;
     /*< public >*/
 
+    QemuMutex lock;
     MemoryRegion iomem;
     uint64_t hpet_offset;
     bool hpet_offset_saved;
@@ -428,6 +430,7 @@ static uint64_t hpet_ram_read(void *opaque, hwaddr addr,
     trace_hpet_ram_read(addr);
     addr &= ~4;
 
+    QEMU_LOCK_GUARD(&s->lock);
     /*address range of all global regs*/
     if (addr <= 0xff) {
         switch (addr) {
@@ -482,6 +485,7 @@ static void hpet_ram_write(void *opaque, hwaddr addr,
     int len = MIN(size * 8, 64 - shift);
     uint64_t old_val, new_val, cleared;
 
+    QEMU_LOCK_GUARD(&s->lock);
     trace_hpet_ram_write(addr, value);
     addr &= ~4;
 
@@ -679,8 +683,10 @@ static void hpet_init(Object *obj)
     SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
     HPETState *s = HPET(obj);
 
+    qemu_mutex_init(&s->lock);
     /* HPET Area */
     memory_region_init_io(&s->iomem, obj, &hpet_ram_ops, s, "hpet", HPET_LEN);
+    memory_region_enable_lockless_io(&s->iomem);
     sysbus_init_mmio(sbd, &s->iomem);
 }