iwlwifi: enable serialization of synchronous commands

Until now it was only possible to have one synchronous command running at
any time. If a synchronous command is in progress when a second request
arrives then the second command will fail. Create a new mutex specific for
this purpose to only allow one synchronous command at a time, but enable
other commands to wait instead of fail if a synchronous command is in
progress.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-dev.h b/drivers/net/wireless/iwlwifi/iwl-dev.h
index f81317d..021c686 100644
--- a/drivers/net/wireless/iwlwifi/iwl-dev.h
+++ b/drivers/net/wireless/iwlwifi/iwl-dev.h
@@ -1111,6 +1111,7 @@
 	spinlock_t hcmd_lock;	/* protect hcmd */
 	spinlock_t reg_lock;	/* protect hw register access */
 	struct mutex mutex;
+	struct mutex sync_cmd_mutex; /* enable serialization of sync commands */
 
 	/* basic pci-network driver stuff */
 	struct pci_dev *pci_dev;