scsi: add a CONFIG_SCSI_MQ_DEFAULT option

Add a Kconfig option to enable the blk-mq path for SCSI by default
to ease testing and deployment in setups that know they benefit
from blk-mq.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Robert Elliott <elliott@hp.com>
Tested-by: Robert Elliott <elliott@hp.com>
diff --git a/drivers/scsi/Kconfig b/drivers/scsi/Kconfig
index 18a3358..71b0877 100644
--- a/drivers/scsi/Kconfig
+++ b/drivers/scsi/Kconfig
@@ -45,6 +45,17 @@
 	default	n
 	select NET
 
+config SCSI_MQ_DEFAULT
+	bool "SCSI: use blk-mq I/O path by default"
+	depends on SCSI
+	---help---
+	  This option enables the new blk-mq based I/O path for SCSI
+	  devices by default.  With the option the scsi_mod.use_blk_mq
+	  module/boot option defaults to Y, without it to N, but it can
+	  still be overriden either way.
+
+	  If unsure say N.
+
 config SCSI_PROC_FS
 	bool "legacy /proc/scsi/ support"
 	depends on SCSI && PROC_FS