mtd: map: fixed bug in 64-bit systems
mtd: map: fixed bug in 64-bit systems

Hardware:
	CPU: XLP832,the 64-bit OS
	NOR Flash:S29GL128S 128M
Software:
	Kernel:2.6.32.41
	Filesystem:JFFS2
When writing files, errors appear:
	Write len 182  but return retlen 180
	Write of 182 bytes at 0x072c815c failed. returned -5, retlen 180
	Write len 186  but return retlen 184
	Write of 186 bytes at 0x072caff4 failed. returned -5, retlen 184
These errors exist only in 64-bit systems,not in 32-bit systems. After analysis, we
found that the left shift operation is wrong in map_word_load_partial. For instance:
	unsigned char buf[3] ={0x9e,0x3a,0xea};
	map_bankwidth(map) is 4;
	for (i=0; i < 3; i++) {
		int bitpos;
		bitpos = (map_bankwidth(map)-1-i)*8;
		orig.x[0] &= ~(0xff << bitpos);
		orig.x[0] |= buf[i] << bitpos;
	}

The value of orig.x[0] is expected to be 0x9e3aeaff, but in this situation(64-bit
System) we'll get the wrong value of 0xffffffff9e3aeaff due to the 64-bit sign
extension:
buf[i] is defined as "unsigned char" and the left-shift operation will convert it
to the type of "signed int", so when left-shift buf[i] by 24 bits, the final result
will get the wrong value: 0xffffffff9e3aeaff.

If the left-shift bits are less than 24, then sign extension will not occur. Whereas
the bankwidth of the nor flash we used is 4, therefore this BUG emerges.

Signed-off-by: Pang Xunlei <8f3df7547938bf466547d5e4573831d5224028fc@zte.com.cn>
Signed-off-by: Zhang Yi <73530dbfda4472fd921974b5ea270e127590f2cc@zte.com.cn>
Signed-off-by: Lu Zhongjun <2260d4a4fd2c1c2f30a4f389e808c461d2a9eb11@zte.com.cn>
Cc: <4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org>
Signed-off-by: Brian Norris <ac73eed4b8a8c9127255a2696c52b2e7503720b8@gmail.com>

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