hw/misc: New "unimplemented" sysbus device

Create a new "unimplemented" sysbus device, which simply accepts
all read and write accesses, and implements them as read-as-zero,
write-ignored, with logging of the access as LOG_UNIMP.

This is useful for stubbing out bits of an SoC or board model
which haven't been written yet.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 1484247815-15279-3-git-send-email-peter.maydell@linaro.org

hw/misc/Makefile.objs

@@ -6,6 +6,8 @@ common-obj-$(CONFIG_SGA) += sga.o
 common-obj-$(CONFIG_ISA_TESTDEV) += pc-testdev.o
 common-obj-$(CONFIG_PCI_TESTDEV) += pci-testdev.o
 
+common-obj-y += unimp.o
+
 obj-$(CONFIG_VMPORT) += vmport.o
 
 # ARM devices

hw/misc/unimp.c

+/* "Unimplemented" device
+ *
+ * This is a dummy device which accepts and logs all accesses.
+ * It's useful for stubbing out regions of an SoC or board
+ * map which correspond to devices that have not yet been
+ * implemented. This is often sufficient to placate initial
+ * guest device driver probing such that the system will
+ * come up.
+ *
+ * Copyright Linaro Limited, 2017
+ * Written by Peter Maydell
+ */
+
+#include "qemu/osdep.h"
+#include "hw/hw.h"
+#include "hw/sysbus.h"
+#include "hw/misc/unimp.h"
+#include "qemu/log.h"
+#include "qapi/error.h"
+
+#define UNIMPLEMENTED_DEVICE(obj) \
+    OBJECT_CHECK(UnimplementedDeviceState, (obj), TYPE_UNIMPLEMENTED_DEVICE)
+
+typedef struct {
+    SysBusDevice parent_obj;
+    MemoryRegion iomem;
+    char *name;
+    uint64_t size;
+} UnimplementedDeviceState;
+
+static uint64_t unimp_read(void *opaque, hwaddr offset, unsigned size)
+{
+    UnimplementedDeviceState *s = UNIMPLEMENTED_DEVICE(opaque);
+
+    qemu_log_mask(LOG_UNIMP, "%s: unimplemented device read "
+                  "(size %d, offset 0x%" HWADDR_PRIx ")\n",
+                  s->name, size, offset);
+    return 0;
+}
+
+static void unimp_write(void *opaque, hwaddr offset,
+                        uint64_t value, unsigned size)
+{
+    UnimplementedDeviceState *s = UNIMPLEMENTED_DEVICE(opaque);
+
+    qemu_log_mask(LOG_UNIMP, "%s: unimplemented device write "
+                  "(size %d, value 0x%" PRIx64
+                  ", offset 0x%" HWADDR_PRIx ")\n",
+                  s->name, size, value, offset);
+}
+
+static const MemoryRegionOps unimp_ops = {
+    .read = unimp_read,
+    .write = unimp_write,
+    .impl.min_access_size = 1,
+    .impl.max_access_size = 8,
+    .valid.min_access_size = 1,
+    .valid.max_access_size = 8,
+    .endianness = DEVICE_NATIVE_ENDIAN,
+};
+
+static void unimp_realize(DeviceState *dev, Error **errp)
+{
+    UnimplementedDeviceState *s = UNIMPLEMENTED_DEVICE(dev);
+
+    if (s->size == 0) {
+        error_setg(errp, "property 'size' not specified or zero");
+        return;
+    }
+
+    if (s->name == NULL) {
+        error_setg(errp, "property 'name' not specified");
+        return;
+    }
+
+    memory_region_init_io(&s->iomem, OBJECT(s), &unimp_ops, s,
+                          s->name, s->size);
+    sysbus_init_mmio(SYS_BUS_DEVICE(s), &s->iomem);
+}
+
+static Property unimp_properties[] = {
+    DEFINE_PROP_UINT64("size", UnimplementedDeviceState, size, 0),
+    DEFINE_PROP_STRING("name", UnimplementedDeviceState, name),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void unimp_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    dc->realize = unimp_realize;
+    dc->props = unimp_properties;
+}
+
+static const TypeInfo unimp_info = {
+    .name = TYPE_UNIMPLEMENTED_DEVICE,
+    .parent = TYPE_SYS_BUS_DEVICE,
+    .instance_size = sizeof(UnimplementedDeviceState),
+    .class_init = unimp_class_init,
+};
+
+static void unimp_register_types(void)
+{
+    type_register_static(&unimp_info);
+}
+
+type_init(unimp_register_types)

include/hw/misc/unimp.h

+/*
+ * "Unimplemented" device
+ *
+ * Copyright Linaro Limited, 2017
+ * Written by Peter Maydell
+ */
+
+#ifndef HW_MISC_UNIMP_H
+#define HW_MISC_UNIMP_H
+
+#define TYPE_UNIMPLEMENTED_DEVICE "unimplemented-device"
+
+/**
+ * create_unimplemented_device: create and map a dummy device
+ * @name: name of the device for debug logging
+ * @base: base address of the device's MMIO region
+ * @size: size of the device's MMIO region
+ *
+ * This utility function creates and maps an instance of unimplemented-device,
+ * which is a dummy device which simply logs all guest accesses to
+ * it via the qemu_log LOG_UNIMP debug log.
+ * The device is mapped at priority -1000, which means that you can
+ * use it to cover a large region and then map other devices on top of it
+ * if necessary.
+ */
+static inline void create_unimplemented_device(const char *name,
+                                               hwaddr base,
+                                               hwaddr size)
+{
+    DeviceState *dev = qdev_create(NULL, TYPE_UNIMPLEMENTED_DEVICE);
+
+    qdev_prop_set_string(dev, "name", name);
+    qdev_prop_set_uint64(dev, "size", size);
+    qdev_init_nofail(dev);
+
+    sysbus_mmio_map_overlap(SYS_BUS_DEVICE(dev), 0, base, -1000);
+}
+
+#endif