drivers/pc80: Add optional spinlock for nvram CBFS access

When enabling the IOMMU on certain systems dmesg is spammed with I/O page faults like the following:
AMD-Vi: Event logged [IO_PAGE_FAULT device=00:14.0 domain=0x000a address=0x000000fdf9103300 flags=0x0030]

Decoding the faulting address:
0x000000fdf9103300
        fdf91x          Hypertransport system management region
              33        SysMgtCmd (System Management Command) = 0x33
              3         Base Command Type = 0x3: STPCLK (Stop Clock request)
               3        SMAF (System Management Action Field) = [3:1] = 0x1
               1        Signal State Bit Map = [0] = 0x1

Therefore, the error appears to be triggered by an upstream C1E request.

This was eventually traced to concurrent access to the SP5100's SPI Flash controller by
multiple APs during startup.  Calls to the nvram read functions get_option and read_option
call CBFS functions, which in turn make near-simultaneous requests to the SPI Flash
controller, thus placing the SP5100 in an invalid state.  This limitation is not documented
in any public AMD errata, and was only discovered through considerable debugging effort.

Change-Id: I4e61b1ab767b1b7958ac7c1cf20eee41d2261bef
Signed-off-by: Timothy Pearson <tpearson@raptorengineeringinc.com>
Reviewed-on: https://review.coreboot.org/12061
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/Kconfig

@@ -480,6 +480,14 @@ config HAVE_ROMSTAGE_CONSOLE_SPINLOCK
 	bool
 	default n
 
+config HAVE_ROMSTAGE_NVRAM_CBFS_SPINLOCK
+	bool
+	default n
+	help
+	  This should be enabled on certain plaforms, such as the AMD
+	  SR565x, that cannot handle concurrent CBFS accesses from
+	  multiple APs during early startup.
+
 config HAVE_MONOTONIC_TIMER
 	def_bool n
 	help

src/arch/x86/include/arch/smp/spinlock.h

@@ -1,7 +1,7 @@
 #ifndef ARCH_SMP_SPINLOCK_H
 #define ARCH_SMP_SPINLOCK_H
 
-#if !defined(__PRE_RAM__) || IS_ENABLED(CONFIG_HAVE_ROMSTAGE_CONSOLE_SPINLOCK)
+#if !defined(__PRE_RAM__) || IS_ENABLED(CONFIG_HAVE_ROMSTAGE_CONSOLE_SPINLOCK) || IS_ENABLED(CONFIG_HAVE_ROMSTAGE_NVRAM_CBFS_SPINLOCK)
 
 /*
  * Your basic SMP spinlocks, allowing only a single CPU anywhere
@@ -14,6 +14,8 @@ typedef struct {
 #ifdef __PRE_RAM__
 spinlock_t *romstage_console_lock(void);
 void initialize_romstage_console_lock(void);
+spinlock_t* romstage_nvram_cbfs_lock(void);
+void initialize_romstage_nvram_cbfs_lock(void);
 #endif
 
 #define SPIN_LOCK_UNLOCKED (spinlock_t) { 1 }

src/cpu/amd/car/post_cache_as_ram.c

@@ -79,6 +79,9 @@ static void prepare_ramstage_region(void *resume_backup_memory)
 #if IS_ENABLED(CONFIG_HAVE_ROMSTAGE_CONSOLE_SPINLOCK)
 	initialize_romstage_console_lock();
 #endif
+#if IS_ENABLED(CONFIG_HAVE_ROMSTAGE_NVRAM_CBFS_SPINLOCK)
+	initialize_romstage_nvram_cbfs_lock();
+#endif
 
 	print_car_debug(" Done\n");
 }

src/drivers/pc80/mc146818rtc.c

@@ -2,6 +2,7 @@
  * This file is part of the coreboot project.
  *
  * Copyright 2014 The Chromium OS Authors. All rights reserved.
+ * Copyright (C) 2015 Timothy Pearson <tpearson@raptorengineeringinc.com>, Raptor Engineering
  *
  * 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
@@ -33,6 +34,16 @@
 #define LB_CKS_LOC		0
 #endif
 
+#include <smp/spinlock.h>
+
+#if (defined(__PRE_RAM__) &&	\
+IS_ENABLED(CONFIG_HAVE_ROMSTAGE_NVRAM_CBFS_SPINLOCK))
+	#define LOCK_NVRAM_CBFS_SPINLOCK spin_lock(romstage_nvram_cbfs_lock());
+	#define UNLOCK_NVRAM_CBFS_SPINLOCK spin_unlock(romstage_nvram_cbfs_lock());
+#else
+	#define LOCK_NVRAM_CBFS_SPINLOCK
+	#define UNLOCK_NVRAM_CBFS_SPINLOCK
+#endif
 
 static void cmos_reset_date(void)
 {
@@ -204,6 +215,8 @@ enum cb_err get_option(void *dest, const char *name)
 	if (!IS_ENABLED(CONFIG_USE_OPTION_TABLE))
 		return CB_CMOS_OTABLE_DISABLED;
 
+	LOCK_NVRAM_CBFS_SPINLOCK
+
 	/* Figure out how long name is */
 	namelen = strnlen(name, CMOS_MAX_NAME_LENGTH);
 
@@ -213,6 +226,8 @@ enum cb_err get_option(void *dest, const char *name)
 	if (!ct) {
 		printk(BIOS_ERR, "RTC: cmos_layout.bin could not be found. "
 						"Options are disabled\n");
+
+		UNLOCK_NVRAM_CBFS_SPINLOCK
 		return CB_CMOS_LAYOUT_NOT_FOUND;
 	}
 	ce = (struct cmos_entries*)((unsigned char *)ct + ct->header_length);
@@ -225,13 +240,19 @@ enum cb_err get_option(void *dest, const char *name)
 	}
 	if (!found) {
 		printk(BIOS_DEBUG, "WARNING: No CMOS option '%s'.\n", name);
+		UNLOCK_NVRAM_CBFS_SPINLOCK
 		return CB_CMOS_OPTION_NOT_FOUND;
 	}
 
-	if (get_cmos_value(ce->bit, ce->length, dest) != CB_SUCCESS)
+	if (get_cmos_value(ce->bit, ce->length, dest) != CB_SUCCESS) {
+		UNLOCK_NVRAM_CBFS_SPINLOCK
 		return CB_CMOS_ACCESS_ERROR;
-	if (!cmos_checksum_valid(LB_CKS_RANGE_START, LB_CKS_RANGE_END, LB_CKS_LOC))
+	}
+	if (!cmos_checksum_valid(LB_CKS_RANGE_START, LB_CKS_RANGE_END, LB_CKS_LOC)) {
+		UNLOCK_NVRAM_CBFS_SPINLOCK
 		return CB_CMOS_CHECKSUM_INVALID;
+	}
+	UNLOCK_NVRAM_CBFS_SPINLOCK
 	return CB_SUCCESS;
 }