acpi: serial: don't use _STA method

The _STA method dates back to the days where we had a static DSDT.  The
device is listed in the DSDT table unconditionally and the _STA method
checks a bit in the isa bridge pci config space to figure whenever a
given is isa device is present or not, then evaluates to 0x0f (present)
or 0x00 (absent).

These days the DSDT is generated by qemu anyway, so if a device is not
present we can simply drop it from the DSDT instead.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200515150421.25479-5-kraxel@redhat.com>

1 files changed, 8 insertions, 24 deletions

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index df5417c75f..cb22cb0fe6 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -1208,50 +1208,34 @@ static Aml *build_lpt_device_aml(void)
     return dev;
 }
 
-static Aml *build_com_device_aml(uint8_t uid)
+static void build_com_device_aml(Aml *scope, uint8_t uid)
 {
     Aml *dev;
     Aml *crs;
-    Aml *method;
-    Aml *if_ctx;
-    Aml *else_ctx;
-    Aml *zero = aml_int(0);
-    Aml *is_present = aml_local(0);
-    const char *enabled_field = "CAEN";
     uint8_t irq = 4;
     uint16_t io_port = 0x03F8;
 
     assert(uid == 1 || uid == 2);
     if (uid == 2) {
-        enabled_field = "CBEN";
         irq = 3;
         io_port = 0x02F8;
     }
+    if (!memory_region_present(get_system_io(), io_port)) {
+        return;
+    }
 
     dev = aml_device("COM%d", uid);
     aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0501")));
     aml_append(dev, aml_name_decl("_UID", aml_int(uid)));
 
-    method = aml_method("_STA", 0, AML_NOTSERIALIZED);
-    aml_append(method, aml_store(aml_name("%s", enabled_field), is_present));
-    if_ctx = aml_if(aml_equal(is_present, zero));
-    {
-        aml_append(if_ctx, aml_return(aml_int(0x00)));
-    }
-    aml_append(method, if_ctx);
-    else_ctx = aml_else();
-    {
-        aml_append(else_ctx, aml_return(aml_int(0x0f)));
-    }
-    aml_append(method, else_ctx);
-    aml_append(dev, method);
+    aml_append(dev, aml_name_decl("_STA", aml_int(0xf)));
 
     crs = aml_resource_template();
     aml_append(crs, aml_io(AML_DECODE16, io_port, io_port, 0x00, 0x08));
     aml_append(crs, aml_irq_no_flags(irq));
     aml_append(dev, aml_name_decl("_CRS", crs));
 
-    return dev;
+    aml_append(scope, dev);
 }
 
 static void build_isa_devices_aml(Aml *table)
@@ -1268,8 +1252,8 @@ static void build_isa_devices_aml(Aml *table)
         aml_append(scope, build_fdc_device_aml(fdc));
     }
     aml_append(scope, build_lpt_device_aml());
-    aml_append(scope, build_com_device_aml(1));
-    aml_append(scope, build_com_device_aml(2));
+    build_com_device_aml(scope, 1);
+    build_com_device_aml(scope, 2);
 
     if (ambiguous) {
         error_report("Multiple ISA busses, unable to define IPMI ACPI data");