hw: virt: Add basic ACPI timer support

For the reduced ACPI platform implement the basic ACPI PM_TMR support.
Implement only the basic counter and not the optional interupt
triggering when the counter's carry changes value.

This is useful for implementing basic timekeeping in early firmware.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

hw/acpi/reduced.c

@@ -132,6 +132,9 @@ static void build_fadt_reduced(GArray *table_data, BIOSLinker *linker,
         .sleep_status_reg = { .space_id = AML_AS_SYSTEM_IO,
                               .bit_width = 8, .bit_offset = 0,
                               .address = ACPI_REDUCED_SLEEP_STATUS_IOPORT },
+        .pm_tmr = { .space_id = AML_AS_SYSTEM_IO,
+                    .bit_width = 32, .bit_offset = 0,
+                    .address = ACPI_REDUCED_PMTIMER_IOPORT },
     };
 
     build_fadt(table_data, linker, &fadt, NULL, NULL);

hw/i386/virt/acpi.c

@@ -57,6 +57,7 @@ typedef struct VirtAcpiState {
     MemoryRegion sleep_iomem;
     MemoryRegion sleep_status_iomem;
     MemoryRegion reset_iomem;
+    MemoryRegion pm_timer_iomem;
 } VirtAcpiState;
 
 #define TYPE_VIRT_ACPI "virt-acpi"
@@ -209,6 +210,25 @@ static const MemoryRegionOps virt_reset_ops = {
     .write = virt_acpi_reset_write,
 };
 
+static void virt_acpi_pm_timer_write(void *opaque, hwaddr addr,
+                                         uint64_t val, unsigned width)
+{
+    return;
+}
+
+static uint64_t virt_acpi_pm_timer_read(void *opaque, hwaddr addr,
+                                            unsigned width)
+{
+    uint64_t counter = muldiv64(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL),
+                                PM_TIMER_FREQUENCY, NANOSECONDS_PER_SECOND);
+    return counter & 0xffffff;
+}
+
+const MemoryRegionOps virt_pm_timer_ops = {
+        .write = virt_acpi_pm_timer_write,
+        .read = virt_acpi_pm_timer_read,
+};
+
 static void virt_device_realize(DeviceState *dev, Error **errp)
 {
     VirtAcpiState *s = VIRT_ACPI(dev);
@@ -236,6 +256,10 @@ static void virt_device_realize(DeviceState *dev, Error **errp)
     memory_region_init_io(&s->reset_iomem, OBJECT(dev),
                           &virt_reset_ops, s, TYPE_VIRT_ACPI, 1);
     sysbus_add_io(sys, ACPI_REDUCED_RESET_IOPORT, &s->reset_iomem);
+
+    memory_region_init_io(&s->pm_timer_iomem, OBJECT(dev), 
+                         &virt_pm_timer_ops, s, TYPE_VIRT_ACPI, 4);
+    sysbus_add_io(sys, ACPI_REDUCED_PMTIMER_IOPORT, &s->pm_timer_iomem);
 }
 
 DeviceState *virt_acpi_init(qemu_irq *gsi, PCIBus *pci_bus)

include/hw/acpi/reduced.h

@@ -7,6 +7,7 @@
 #define ACPI_REDUCED_SLEEP_STATUS_IOPORT 0x3D0
 #define ACPI_REDUCED_RESET_IOPORT	  0x3C0
 #define ACPI_REDUCED_RESET_VALUE	  4
+#define ACPI_REDUCED_PMTIMER_IOPORT   0x3E0
 
 void acpi_reduced_setup(MachineState *machine, AcpiConfiguration *conf);