acpi: pc: add fw_cfg device node to dsdt

Add a fw_cfg device node to the ACPI DSDT. While the guest-side
firmware can't utilize this information (since it has to access
the hard-coded fw_cfg device to extract ACPI tables to begin with),
having fw_cfg listed in ACPI will help the guest kernel keep a more
accurate inventory of in-use IO port regions.
Signed-off-by: NGabriel Somlo <somlo@cmu.edu>
Reviewed-by: NLaszlo Ersek <lersek@redhat.com>
Reviewed-by: NMarc Marí <markmb@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Message-id: 1455906029-25565-4-git-send-email-somlo@cmu.edu
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/i386/acpi-build.c

@@ -2190,6 +2190,35 @@ build_dsdt(GArray *table_data, GArray *linker,
     aml_append(scope, aml_name_decl("_S5", pkg));
     aml_append(dsdt, scope);
 
+    /* create fw_cfg node, unconditionally */
+    {
+        /* when using port i/o, the 8-bit data register *always* overlaps
+         * with half of the 16-bit control register. Hence, the total size
+         * of the i/o region used is FW_CFG_CTL_SIZE; when using DMA, the
+         * DMA control register is located at FW_CFG_DMA_IO_BASE + 4 */
+        uint8_t io_size = object_property_get_bool(OBJECT(pcms->fw_cfg),
+                                                   "dma_enabled", NULL) ?
+                          ROUND_UP(FW_CFG_CTL_SIZE, 4) + sizeof(dma_addr_t) :
+                          FW_CFG_CTL_SIZE;
+
+        scope = aml_scope("\\_SB.PCI0");
+        dev = aml_device("FWCF");
+
+        aml_append(dev, aml_name_decl("_HID", aml_string("QEMU0002")));
+
+        /* device present, functioning, decoding, not shown in UI */
+        aml_append(dev, aml_name_decl("_STA", aml_int(0xB)));
+
+        crs = aml_resource_template();
+        aml_append(crs,
+            aml_io(AML_DECODE16, FW_CFG_IO_BASE, FW_CFG_IO_BASE, 0x01, io_size)
+        );
+        aml_append(dev, aml_name_decl("_CRS", crs));
+
+        aml_append(scope, dev);
+        aml_append(dsdt, scope);
+    }
+
     if (misc->applesmc_io_base) {
         scope = aml_scope("\\_SB.PCI0.ISA");
         dev = aml_device("SMC");