MPC5200: workaround data corruption for unaligned local bus accesses

The MPC5200 has a nasty problem that will cause silent data corruption
when performing unaligned 16 or 32 byte accesses when reading from the
local bus - typically this affects reading from flash. The problem can
be easily shown:

=> md fc0c0000 10
fc0c0000: 323e4337 01626f6f 74636d64 3d72756e    2>C7.bootcmd=run
fc0c0010: 206e6574 5f6e6673 00626f6f 7464656c     net_nfs.bootdel
fc0c0020: 61793d35 00626175 64726174 653d3131    ay=5.baudrate=11
fc0c0030: 35323030 00707265 626f6f74 3d656368    5200.preboot=ech
=> md fc0c0001 10
fc0c0001: 65636801 00000074 0000003d 00000020    ech....t...=...
fc0c0011: 0000005f 00000000 00000074 00000061    ..._.......t...a
fc0c0021: 00000000 00000064 00000065 00000035    .......d...e...5
fc0c0031: 00000000 00000062 0000003d 0000006f    .......b...=...o
=> md.w fc0c0001 10
fc0c0001: 0000 3701 0000 6f74 0000 643d 0000 6e20    ..7...ot..d=..n
fc0c0011: 0000 745f 0000 7300 0000 6f74 0000 6c61    ..t_..s...ot..la

This commit implements a workaround at least for the most blatant
problem: using memcpy() from NOR flash. We rename the assembler
routine into __memcpy() and provide a wrapper, which will use a
byte-wise copy loop for unaligned source or target addresses when
reading from NOR flash, and branch to the optimized __memcpy()
in all other cases, thus minimizing the performance impact.

Tested on lite5200b and TQM5200S.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Detlev Zundel <dzu@denx.de>

arch/powerpc/cpu/mpc5xxx/Makefile

@@ -30,6 +30,11 @@ SOBJS	= io.o firmware_sc_task_bestcomm.impl.o
 COBJS	= i2c.o traps.o cpu.o cpu_init.o ide.o interrupts.o \
 	  loadtask.o pci_mpc5200.o serial.o speed.o usb_ohci.o usb.o
 
+# Workaround for local bus unaligned access problem on MPC5200
+#ifdef CONFIG_MPC5200
+COBJS	+= memcpy_mpc5200.o
+#endif
+
 SRCS	:= $(START:.o=.S) $(SOBJS:.o=.S) $(COBJS:.o=.c)
 OBJS	:= $(addprefix $(obj),$(SOBJS) $(COBJS))
 START	:= $(addprefix $(obj),$(START))

arch/powerpc/cpu/mpc5xxx/memcpy_mpc5200.c

@@ -0,0 +1,71 @@
+/*
+ * (C) Copyright 2010
+ * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * 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 (at your option) 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., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+/*
+ * This is a workaround for issues on the MPC5200, where unaligned
+ * 32-bit-accesses to the local bus will deliver corrupted data. This
+ * happens for example when trying to use memcpy() from an odd NOR
+ * flash address; the behaviour can be also seen when using "md" on an
+ * odd NOR flash address (but there it is not a bug in U-Boot, which
+ * only shows the behaviour of this processor).
+ *
+ * For memcpy(), we test if either the source or the target address
+ * are not 32 bit aligned, and - if so - if the source address is in
+ * NOR flash: in this case we perform a byte-wise (slow) then; for
+ * aligned operations of non-flash areas we use the optimized (fast)
+ * real __memcpy().  This way we minimize the performance impact of
+ * this workaround.
+ *
+ */
+
+#include <common.h>
+#include <flash.h>
+#include <linux/types.h>
+
+void *memcpy(void *trg, const void *src, size_t len)
+{
+	extern void* __memcpy(void *, const void *, size_t);
+	char *s = (char *)src;
+	char *t = (char *)trg;
+	void *dest = (void *)src;
+
+	/*
+	 * Check is source address is in flash:
+	 * If not, we use the fast assembler code
+	 */
+	if (((((unsigned long)s & 3) == 0)	/* source aligned  */
+		&&				/*	AND	   */
+	     (((unsigned long)t & 3) == 0))	/* target aligned, */
+		||				/*	or	   */
+	    (addr2info((ulong)s) == NULL)) {	/* source not in flash */
+		return __memcpy(trg, src, len);
+	}
+
+	/*
+	 * Copying from flash, perform byte by byte copy.
+	 */
+	while (len-- > 0)
+		*t++ = *s++;
+
+	return dest;
+}

arch/powerpc/lib/Makefile

@@ -43,6 +43,11 @@ COBJS-y	+= time.o
 SRCS	:= $(SOBJS-y:.o=.S) $(COBJS-y:.o=.c)
 OBJS	:= $(addprefix $(obj),$(SOBJS-y) $(COBJS-y))
 
+# Workaround for local bus unaligned access problem on MPC5200
+ifdef CONFIG_MPC5200
+$(obj)ppcstring.o: AFLAGS += -Dmemcpy=__memcpy
+endif
+
 $(LIB):	$(obj).depend $(OBJS)
 	@if ! $(CROSS_COMPILE)readelf -S $(OBJS) | grep -q '\.fixup.*PROGBITS';\
 	then \