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

include/hw/misc/unimp.h

@@ -0,0 +1,39 @@
+/*
+ * "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