iwlwifi: allow to zero SRAM

Sending a NULL pointer to iwl_trans_write_mem allows now
to zero SRAM.
Signed-off-by: NEmmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

drivers/net/wireless/iwlwifi/iwl-trans.h

@@ -391,7 +391,8 @@ struct iwl_trans;
  * @read_prph: read a DWORD from a periphery register
  * @write_prph: write a DWORD to a periphery register
  * @read_mem: read device's SRAM in DWORD
- * @write_mem: write device's SRAM in DWORD
+ * @write_mem: write device's SRAM in DWORD. If %buf is %NULL, then the memory
+ *	will be zeroed.
  * @configure: configure parameters required by the transport layer from
  *	the op_mode. May be called several times before start_fw, can't be
  *	called after that.

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

@@ -815,7 +815,8 @@ static int iwl_trans_pcie_write_mem(struct iwl_trans *trans, u32 addr,
 	if (iwl_trans_grab_nic_access(trans, false)) {
 		iwl_write32(trans, HBUS_TARG_MEM_WADDR, addr);
 		for (offs = 0; offs < dwords; offs++)
-			iwl_write32(trans, HBUS_TARG_MEM_WDAT, vals[offs]);
+			iwl_write32(trans, HBUS_TARG_MEM_WDAT,
+				    vals ? vals[offs] : 0);
 		iwl_trans_release_nic_access(trans);
 	} else {
 		ret = -EBUSY;