e1000e: ignore factory-default checksum value on TGP platform

As described by Vitaly Lifshits:

> Starting from Tiger Lake, LAN NVM is locked for writes by SW, so the
> driver cannot perform checksum validation and correction. This means
> that all NVM images must leave the factory with correct checksum and
> checksum valid bit set.

Unfortunately some systems have left the factory with an empty checksum.
NVM is not modifiable on this platform, hence ignore checksum 0xFFFF on
Tiger Lake systems to work around this.

Signed-off-by: Jacek Kowalski <[email protected]>
Fixes: 4051f68 ("e1000e: Do not take care about recovery NVM checksum")
Cc: [email protected]
Reviewed-by: Simon Horman <[email protected]>
Signed-off-by: NipaLocal <nipa@local>

Author: jacekkow

drivers/net/ethernet/intel/e1000e/defines.h

@@ -637,6 +637,7 @@
 
 /* For checksumming, the sum of all words in the NVM should equal 0xBABA. */
 #define NVM_SUM                    0xBABA
+#define NVM_SUM_FACTORY_DEFAULT    0xFFFF
 
 /* PBA (printed board assembly) number words */
 #define NVM_PBA_OFFSET_0           8

drivers/net/ethernet/intel/e1000e/nvm.c

@@ -558,6 +558,11 @@ s32 e1000e_validate_nvm_checksum_generic(struct e1000_hw *hw)
 		checksum += nvm_data;
 	}
 
+	if (hw->mac.type == e1000_pch_tgp && checksum == (u16)NVM_SUM_FACTORY_DEFAULT) {
+		e_dbg("Factory-default NVM Checksum on TGP platform - ignoring\n");
+		return 0;
+	}
+
 	if (checksum != (u16)NVM_SUM) {
 		e_dbg("NVM Checksum Invalid\n");
 		return -E1000_ERR_NVM;