OvmfPkg/CpuHotplugSmm: add hotplug register block helper functions

Add a handful of simple functions for accessing QEMU's hotplug registers
more conveniently. These functions thinly wrap some of the registers
described in "docs/specs/acpi_cpu_hotplug.txt" in the QEMU tree. The
functions hang (by design) if they encounter an internal failure.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1512
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200226221156.29589-8-lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Tested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

OvmfPkg/CpuHotplugSmm/QemuCpuhp.h

@@ -0,0 +1,47 @@
+/** @file
+  Simple wrapper functions that access QEMU's modern CPU hotplug register
+  block.
+
+  These functions thinly wrap some of the registers described in
+  "docs/specs/acpi_cpu_hotplug.txt" in the QEMU source. IO Ports are accessed
+  via EFI_MM_CPU_IO_PROTOCOL. If a protocol call fails, these functions don't
+  return.
+
+  Copyright (c) 2020, Red Hat, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+#ifndef QEMU_CPUHP_H_
+#define QEMU_CPUHP_H_
+
+#include <Protocol/MmCpuIo.h>  // EFI_MM_CPU_IO_PROTOCOL
+
+UINT32
+QemuCpuhpReadCommandData2 (
+  IN CONST EFI_MM_CPU_IO_PROTOCOL *MmCpuIo
+  );
+
+UINT8
+QemuCpuhpReadCpuStatus (
+  IN CONST EFI_MM_CPU_IO_PROTOCOL *MmCpuIo
+  );
+
+UINT32
+QemuCpuhpReadCommandData (
+  IN CONST EFI_MM_CPU_IO_PROTOCOL *MmCpuIo
+  );
+
+VOID
+QemuCpuhpWriteCpuSelector (
+  IN CONST EFI_MM_CPU_IO_PROTOCOL *MmCpuIo,
+  IN UINT32                       Selector
+  );
+
+VOID
+QemuCpuhpWriteCommand (
+  IN CONST EFI_MM_CPU_IO_PROTOCOL *MmCpuIo,
+  IN UINT8                        Command
+  );
+
+#endif // QEMU_CPUHP_H_