arm: add fw_cfg to "virt" board

fw_cfg already supports exposure over MMIO (used in ppc/mac_newworld.c,
ppc/mac_oldworld.c, sparc/sun4m.c); we can easily add it to the "virt"
board.

Because MMIO access is slow on ARM KVM, we enable the guest, with
fw_cfg_init_mem_wide(), to transfer up to 8 bytes with a single access.
This has been measured to speed up transfers up to 7.5-fold, relative to
single byte data access, on both ARM KVM and x86_64 TCG.

The MMIO register block of fw_cfg is advertized in the device tree. As
base address we pick 0x09020000, which conforms to the comment preceding
"a15memmap": it falls in the miscellaneous device I/O range 128MB..256MB,
and it is aligned at 64KB. The DTB properties follow the documentation in
the Linux source file "Documentation/devicetree/bindings/arm/fw-cfg.txt".

fw_cfg automatically exports a number of files to the guest; for example,
"bootorder" (see fw_cfg_machine_reset()).

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1419250305-31062-9-git-send-email-pbonzini@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/arm/virt.c

@@ -68,6 +68,7 @@ enum {
     VIRT_UART,
     VIRT_MMIO,
     VIRT_RTC,
+    VIRT_FW_CFG,
 };
 
 typedef struct MemMapEntry {
@@ -125,6 +126,7 @@ static const MemMapEntry a15memmap[] = {
     [VIRT_GIC_CPU] =    { 0x08010000, 0x00010000 },
     [VIRT_UART] =       { 0x09000000, 0x00001000 },
     [VIRT_RTC] =        { 0x09010000, 0x00001000 },
+    [VIRT_FW_CFG] =     { 0x09020000, 0x0000000a },
     [VIRT_MMIO] =       { 0x0a000000, 0x00000200 },
     /* ...repeating for a total of NUM_VIRTIO_TRANSPORTS, each of that size */
     /* 0x10000000 .. 0x40000000 reserved for PCI */
@@ -537,6 +539,23 @@ static void create_flash(const VirtBoardInfo *vbi)
     g_free(nodename);
 }
 
+static void create_fw_cfg(const VirtBoardInfo *vbi)
+{
+    hwaddr base = vbi->memmap[VIRT_FW_CFG].base;
+    hwaddr size = vbi->memmap[VIRT_FW_CFG].size;
+    char *nodename;
+
+    fw_cfg_init_mem_wide(base + 8, base, 8);
+
+    nodename = g_strdup_printf("/fw-cfg@%" PRIx64, base);
+    qemu_fdt_add_subnode(vbi->fdt, nodename);
+    qemu_fdt_setprop_string(vbi->fdt, nodename,
+                            "compatible", "qemu,fw-cfg-mmio");
+    qemu_fdt_setprop_sized_cells(vbi->fdt, nodename, "reg",
+                                 2, base, 2, size);
+    g_free(nodename);
+}
+
 static void *machvirt_dtb(const struct arm_boot_info *binfo, int *fdt_size)
 {
     const VirtBoardInfo *board = (const VirtBoardInfo *)binfo;
@@ -627,6 +646,8 @@ static void machvirt_init(MachineState *machine)
      */
     create_virtio_devices(vbi, pic);
 
+    create_fw_cfg(vbi);
+
     vbi->bootinfo.ram_size = machine->ram_size;
     vbi->bootinfo.kernel_filename = machine->kernel_filename;
     vbi->bootinfo.kernel_cmdline = machine->kernel_cmdline;