x86: add cache-as-ram migration option

There are some boards that do a significant amount of
work after cache-as-ram is torn down but before ramstage
is loaded. For example, using vboot to verify the ramstage
is one such operation. However, there are pieces of code
that are executed that reference global variables that
are linked in the cache-as-ram region. If those variables
are referenced after cache-as-ram is torn down then the
values observed will most likely be incorrect.

Therefore provide a Kconfig option to select cache-as-ram
migration to memory using cbmem. This option is named
CAR_MIGRATION. When enabled, the address of cache-as-ram
variables may be obtained dynamically. Additionally,
when cache-as-ram migration occurs the cache-as-ram
data region for global variables is copied into cbmem.
There are also automatic callbacks for other modules
to perform their own migration, if necessary.

Change-Id: I2e77219647c2bd2b1aa845b262be3b2543f1fcb7
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/3232
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/cpu/x86/Kconfig

@@ -115,3 +115,12 @@ config X86_AMD_FIXED_MTRRS
 	help
 	  This option informs the MTRR code to use the RdMem and WrMem fields
 	  in the fixed MTRR MSRs.
+
+config CAR_MIGRATION
+	def_bool n
+	depends on DYNAMIC_CBMEM || EARLY_CBMEM_INIT
+	help
+	  Migrate the cache-as-ram variables to CBMEM once CBMEM is set up
+	  in romstage. This option is only needed if one will be doing more
+	  work in romstage after the cache-as-ram is torn down aside from
+	  loading ramstage.

src/cpu/x86/Makefile.inc

@@ -0,0 +1 @@
+romstage-$(CONFIG_CAR_MIGRATION) += car.c

src/cpu/x86/car.c

@@ -0,0 +1,101 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2013 Google, Inc.
+ *
+ * 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; version 2 of the License.
+ *
+ * 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 St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <string.h>
+#include <stddef.h>
+#include <console/console.h>
+#include <cbmem.h>
+#include <cpu/x86/car.h>
+
+typedef void (* const car_migration_func_t)(void);
+
+extern car_migration_func_t _car_migrate_start;
+extern car_migration_func_t _car_migrate_end;
+
+extern char _car_data_start[];
+extern char _car_data_end[];
+
+/*
+ * The car_migrated global variable determines if the cache-as-ram space has
+ * been migrated to real RAM. It does this by asumming the following things:
+ *   1. cache-as-ram space is zero'd out once it is set up.
+ *   2. Either the cache-as-ram space is memory-backed after getting torn down
+ *      or the space returns 0xff's for each byte read.
+ * Based on these 2 attributes there is the ability to tell when the
+ * cache-as-ram region has been migrated.
+ */
+static int car_migrated CAR_GLOBAL;
+
+
+void *car_get_var_ptr(void *var)
+{
+	char *migrated_base;
+	int offset;
+	void * _car_start = &_car_data_start;
+	void * _car_end = &_car_data_end;
+
+	/* If the cache-as-ram has not been migrated return the pointer
+	 * passed in. */
+	if (!car_migrated)
+		return var;
+
+	if (var < _car_start || var >= _car_end) {
+		printk(BIOS_ERR,
+		       "Requesting CAR variable outside of CAR region: %p\n",
+		       var);
+		return var;
+	}
+
+	migrated_base = cbmem_find(CBMEM_ID_CAR_GLOBALS);
+
+	if (migrated_base == NULL) {
+		printk(BIOS_ERR, "CAR: Could not find migration base!\n");
+		return var;
+	}
+
+	offset = (char *)var - (char *)_car_start;
+
+	return &migrated_base[offset];
+}
+
+void car_migrate_variables(void)
+{
+	void *migrated_base;
+	car_migration_func_t *migrate_func;
+	size_t car_data_size = &_car_data_end[0] - &_car_data_start[0];
+
+	migrated_base = cbmem_add(CBMEM_ID_CAR_GLOBALS, car_data_size);
+
+	if (migrated_base == NULL) {
+		printk(BIOS_ERR, "Could not migrate CAR data!\n");
+		return;
+	}
+
+	memcpy(migrated_base, &_car_data_start[0], car_data_size);
+
+	/* Mark that the data has been moved. */
+	car_migrated = ~0;
+
+	/* Call all the migration functions. */
+	migrate_func = &_car_migrate_start;
+	while (migrate_func != &_car_migrate_end) {
+		(*migrate_func)();
+		migrate_func++;
+	}
+}