p54: improve eeprom parser

Like other vendors, p54* devices have a checksum for
the EEPROM descriptor data. This patch enhances the
parser code to generate and verify the data fields,
before initializing the radio-chip on the card.

Note:
	If you have to bootstrap an alternative EEPROM image
	for your device and you don't know how to generate a
	valid crc ccitt checksum, you should take a look at:
	http://git.kernel.org/?p=linux/kernel/git/chr/p54tools.git

	The "checksum" utility loads a binary p54 EEPROM blob
	(use the -f switch, to skip the check) and applies
	the correct crc automatically.
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/p54/Kconfig

@@ -2,6 +2,7 @@ config P54_COMMON
 	tristate "Softmac Prism54 support"
 	depends on MAC80211 && EXPERIMENTAL
 	select FW_LOADER
+	select CRC_CCITT
 	---help---
 	  This is common code for isl38xx/stlc45xx based modules.
 	  This module does nothing by itself - the USB/PCI/SPI front-ends

drivers/net/wireless/p54/eeprom.c

@@ -23,6 +23,7 @@
 #include <linux/slab.h>
 
 #include <net/mac80211.h>
+#include <linux/crc-ccitt.h>
 
 #include "p54.h"
 #include "eeprom.h"
@@ -540,6 +541,7 @@ int p54_parse_eeprom(struct ieee80211_hw *dev, void *eeprom, int len)
 	int err;
 	u8 *end = (u8 *)eeprom + len;
 	u16 synth = 0;
+	u16 crc16 = ~0;
 
 	wrap = (struct eeprom_pda_wrap *) eeprom;
 	entry = (void *)wrap->data + le16_to_cpu(wrap->len);
@@ -655,16 +657,29 @@ int p54_parse_eeprom(struct ieee80211_hw *dev, void *eeprom, int len)
 			}
 			break;
 		case PDR_END:
-			/* make it overrun */
-			entry_len = len;
+			crc16 = ~crc_ccitt(crc16, (u8 *) entry, sizeof(*entry));
+			if (crc16 != le16_to_cpup((__le16 *)entry->data)) {
+				wiphy_err(dev->wiphy, "eeprom failed checksum "
+					 "test!\n");
+				err = -ENOMSG;
+				goto err;
+			} else {
+				goto good_eeprom;
+			}
 			break;
 		default:
 			break;
 		}
 
-		entry = (void *)entry + (entry_len + 1)*2;
+		crc16 = crc_ccitt(crc16, (u8 *)entry, (entry_len + 1) * 2);
+		entry = (void *)entry + (entry_len + 1) * 2;
 	}
 
+	wiphy_err(dev->wiphy, "unexpected end of eeprom data.\n");
+	err = -ENODATA;
+	goto err;
+
+good_eeprom:
 	if (!synth || !priv->iq_autocal || !priv->output_limit ||
 	    !priv->curve_data) {
 		wiphy_err(dev->wiphy,