[efi] Centralise definition of efi_cpu_nap()

Define a cpu_halt() function which is architecture-specific but
platform-independent, and merge the multiple architecture-specific
implementations of the EFI cpu_nap() function into a single central
efi_cpu_nap() that uses cpu_halt() if applicable.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/interface/efi/efi_nap.c

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2008 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <ipxe/nap.h>
+#include <ipxe/efi/efi.h>
+
+/** @file
+ *
+ * iPXE CPU sleeping API for EFI
+ *
+ */
+
+/**
+ * Sleep until next interrupt
+ *
+ */
+static void efi_cpu_nap ( void ) {
+	/*
+	 * I can't find any EFI API that allows us to put the CPU to
+	 * sleep.  The CpuSleep() function is defined in CpuLib.h, but
+	 * isn't part of any exposed protocol so we have no way to
+	 * call it.
+	 *
+	 * The EFI shell doesn't seem to bother sleeping the CPU; it
+	 * just sits there idly burning power.
+	 *
+	 * If a shutdown is in progess, there may be nothing to
+	 * generate an interrupt since the timer is disabled in the
+	 * first step of ExitBootServices().
+	 */
+	if ( ! efi_shutdown_in_progress )
+		cpu_halt();
+}
+
+PROVIDE_NAP ( efi, cpu_nap, efi_cpu_nap );