e1000e: fix timing for 82579 Gigabit Ethernet controller

After an upgrade to Linux kernel v4.x the hardware timestamps of the
82579 Gigabit Ethernet Controller are different than expected.
The values that are being read are almost four times as big as before
the kernel upgrade.

The difference is that after the upgrade the driver sets the clock
frequency to 25MHz, where before the upgrade it was set to 96MHz. Intel
confirmed that the correct frequency for this network adapter is 96MHz.
Signed-off-by: NBernd Faust <berndfaust@gmail.com>
Acked-by: NSasha Neftin <sasha.neftin@intel.com>
Acked-by: NJacob Keller <jacob.e.keller@intel.com>
Tested-by: NAaron Brown <aaron.f.brown@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

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

@@ -3511,6 +3511,12 @@ s32 e1000e_get_base_timinca(struct e1000_adapter *adapter, u32 *timinca)
 
 	switch (hw->mac.type) {
 	case e1000_pch2lan:
+		/* Stable 96MHz frequency */
+		incperiod = INCPERIOD_96MHz;
+		incvalue = INCVALUE_96MHz;
+		shift = INCVALUE_SHIFT_96MHz;
+		adapter->cc.shift = shift + INCPERIOD_SHIFT_96MHz;
+		break;
 	case e1000_pch_lpt:
 		if (er32(TSYNCRXCTL) & E1000_TSYNCRXCTL_SYSCFI) {
 			/* Stable 96MHz frequency */