iwlwifi: don't panic in error path on non-msix systems

The driver uses msix causes-register to handle both msix and non msix
interrupts when performing sync nmi.  On devices that do not support
msix this register is unmapped and accessing it causes a kernel panic.

Solve this by differentiating the two cases and accessing the proper
causes-register in each case.
Reported-by: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Shahar S Matityahu <shahar.s.matityahu@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/pcie/trans.c

@@ -3644,20 +3644,27 @@ struct iwl_trans *iwl_trans_pcie_alloc(struct pci_dev *pdev,
 
 void iwl_trans_pcie_sync_nmi(struct iwl_trans *trans)
 {
+	struct iwl_trans_pcie *trans_pcie = IWL_TRANS_GET_PCIE_TRANS(trans);
 	unsigned long timeout = jiffies + IWL_TRANS_NMI_TIMEOUT;
+	u32 inta_addr, sw_err_bit;
+
+	if (trans_pcie->msix_enabled) {
+		inta_addr = CSR_MSIX_HW_INT_CAUSES_AD;
+		sw_err_bit = MSIX_HW_INT_CAUSES_REG_SW_ERR;
+	} else {
+		inta_addr = CSR_INT;
+		sw_err_bit = CSR_INT_BIT_SW_ERR;
+	}
 
 	iwl_disable_interrupts(trans);
 	iwl_force_nmi(trans);
 	while (time_after(timeout, jiffies)) {
-		u32 inta_hw = iwl_read32(trans,
-					 CSR_MSIX_HW_INT_CAUSES_AD);
+		u32 inta_hw = iwl_read32(trans, inta_addr);
 
 		/* Error detected by uCode */
-		if (inta_hw & MSIX_HW_INT_CAUSES_REG_SW_ERR) {
+		if (inta_hw & sw_err_bit) {
 			/* Clear causes register */
-			iwl_write32(trans, CSR_MSIX_HW_INT_CAUSES_AD,
-				    inta_hw &
-				    MSIX_HW_INT_CAUSES_REG_SW_ERR);
+			iwl_write32(trans, inta_addr, inta_hw & sw_err_bit);
 			break;
 		}