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diff --git a/Documentation/pcmcia/devicetable.txt b/Documentation/pcmcia/devicetable.txt
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+Matching of PCMCIA devices to drivers is done using one or more of the
+following criteria:
+
+- manufactor ID
+- card ID
+- product ID strings _and_ hashes of these strings
+- function ID
+- device function (actual and pseudo)
+
+You should use the helpers in include/pcmcia/device_id.h for generating the
+struct pcmcia_device_id[] entries which match devices to drivers.
+
+If you want to match product ID strings, you also need to pass the crc32
+hashes of the string to the macro, e.g. if you want to match the product ID
+string 1, you need to use
+
+PCMCIA_DEVICE_PROD_ID1("some_string", 0x(hash_of_some_string)),
+
+If the hash is incorrect, the kernel will inform you about this in "dmesg"
+upon module initialization, and tell you of the correct hash.
+
+You can determine the hash of the product ID strings by catting the file
+"modalias" in the sysfs directory of the PCMCIA device. It generates a string
+in the following form:
+pcmcia:m0149cC1ABf06pfn00fn00pa725B842DpbF1EFEE84pc0877B627pd00000000
+
+The hex value after "pa" is the hash of product ID string 1, after "pb" for
+string 2 and so on.
+
+Alternatively, you can use this small tool to determine the crc32 hash.
+simply pass the string you want to evaluate as argument to this program,
+e.g.
+$ ./crc32hash "Dual Speed"
+
+-------------------------------------------------------------------------
+/* crc32hash.c - derived from linux/lib/crc32.c, GNU GPL v2 */
+#include <string.h>
+#include <stdio.h>
+#include <ctype.h>
+#include <stdlib.h>
+
+unsigned int crc32(unsigned char const *p, unsigned int len)
+{
+	int i;
+	unsigned int crc = 0;
+	while (len--) {
+		crc ^= *p++;
+		for (i = 0; i < 8; i++)
+			crc = (crc >> 1) ^ ((crc & 1) ? 0xedb88320 : 0);
+	}
+	return crc;
+}
+
+int main(int argc, char **argv) {
+	unsigned int result;
+	if (argc != 2) {
+		printf("no string passed as argument\n");
+		return -1;
+	}
+	result = crc32(argv[1], strlen(argv[1]));
+	printf("0x%x\n", result);
+	return 0;
+}