NVMe: Make I/O timeout a module parameter

Increase the default timeout to 30 seconds to match SCSI.

Signed-off-by: Keith Busch <keith.busch@intel.com>
[use byte instead of ushort]
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
diff --git a/include/linux/nvme.h b/include/linux/nvme.h
index 15d071e..1da0807 100644
--- a/include/linux/nvme.h
+++ b/include/linux/nvme.h
@@ -66,7 +66,8 @@
 
 #define NVME_VS(major, minor)	(major << 16 | minor)
 
-#define NVME_IO_TIMEOUT	(5 * HZ)
+extern unsigned char io_timeout;
+#define NVME_IO_TIMEOUT	(io_timeout * HZ)
 
 /*
  * Represents an NVM Express device.  Each nvme_dev is a PCI function.