Add support for etc/hardware-info fw_cfg file

edk2 looks for the etc/hardware-info fw_cfg file to discover hardware
which can not easily be found in other ways.  Entries consist of a
header with hardware type and entry size (HARDWARE_INFO_HEADER),
followed by the actual hardware description (which is type specific).
The file can have multiple entries.

This patch adds the infrastructure to add entries to the file and an
entry struct for simple devices (HARDWARE_INFO_SIMPLE_DEVICE) which have
an mmio address only.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-ID: <20250225163031.1409078-2-kraxel@redhat.com>

hw/uefi/hardware-info.c

@@ -0,0 +1,31 @@
+/*
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * pass hardware information to uefi
+ *
+ * see OvmfPkg/Library/HardwareInfoLib/ in edk2
+ */
+
+#include "qemu/osdep.h"
+
+#include "hw/nvram/fw_cfg.h"
+#include "hw/uefi/hardware-info.h"
+
+static void      *blob;
+static uint64_t  blobsize;
+
+void hardware_info_register(HARDWARE_INFO_TYPE type, void *info, uint64_t infosize)
+{
+    HARDWARE_INFO_HEADER hdr = {
+        .type.value = cpu_to_le64(type),
+        .size       = cpu_to_le64(infosize),
+    };
+
+    blob = g_realloc(blob, blobsize + sizeof(hdr) + infosize);
+    memcpy(blob + blobsize, &hdr, sizeof(hdr));
+    blobsize += sizeof(hdr);
+    memcpy(blob + blobsize, info, infosize);
+    blobsize += infosize;
+
+    fw_cfg_modify_file(fw_cfg_find(), "etc/hardware-info", blob, blobsize);
+}

hw/uefi/meson.build

@@ -0,0 +1 @@
+system_ss.add(files('hardware-info.c'))

include/hw/uefi/hardware-info.h

@@ -0,0 +1,35 @@
+/*
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * pass hardware information to uefi
+ *
+ * see OvmfPkg/Library/HardwareInfoLib/ in edk2
+ */
+#ifndef QEMU_UEFI_HARDWARE_INFO_H
+#define QEMU_UEFI_HARDWARE_INFO_H
+
+/* data structures */
+
+typedef enum {
+    HardwareInfoTypeUndefined  = 0,
+    HardwareInfoTypeHostBridge = 1,
+    HardwareInfoQemuUefiVars   = 2,
+} HARDWARE_INFO_TYPE;
+
+typedef struct {
+    union {
+        uint64_t            uint64;
+        HARDWARE_INFO_TYPE  value;
+    } type;
+    uint64_t  size;
+} HARDWARE_INFO_HEADER;
+
+typedef struct {
+    uint64_t  mmio_address;
+} HARDWARE_INFO_SIMPLE_DEVICE;
+
+/* qemu functions */
+
+void hardware_info_register(HARDWARE_INFO_TYPE type, void *info, uint64_t size);
+
+#endif /* QEMU_UEFI_HARDWARE_INFO_H */