iwlwifi: pcie: Enable MSI mode when using MSI interrupts

On some of the chipsets MSI & INTA interrupts are disabled by default in
the HW registers, and need to be explicitly enabled to be used.

In case MSI-X isn't used, make sure MSI mode is enabled by setting
the relevant HW register.
Signed-off-by: Ido Yariv <idox.yariv@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/iwl-prph.h

@@ -417,5 +417,6 @@ enum {
 };
 
 #define UREG_CHICK		(0xA05C00)
+#define UREG_CHICK_MSI_ENABLE	BIT(24)
 #define UREG_CHICK_MSIX_ENABLE	BIT(25)
 #endif				/* __iwl_prph_h__ */

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

@@ -1396,8 +1396,12 @@ static void iwl_pcie_init_msix(struct iwl_trans_pcie *trans_pcie)
 
 	max_rx_vector = trans_pcie->allocated_vector - 1;
 
-	if (!trans_pcie->msix_enabled)
+	if (!trans_pcie->msix_enabled) {
+		if (trans->cfg->mq_rx_supported)
+			iwl_write_prph(trans, UREG_CHICK,
+				       UREG_CHICK_MSI_ENABLE);
 		return;
+	}
 
 	iwl_write_prph(trans, UREG_CHICK, UREG_CHICK_MSIX_ENABLE);