NVMe: Add nvme subsystem reset IOCTL

Controllers can perform optional subsystem resets as introduced in NVMe
1.1. This patch adds an IOCTL to trigger the subsystem reset by writing
"NVMe" to the NSSR register.
Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
Acked-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/block/nvme-core.c

@@ -1901,6 +1901,15 @@ static int nvme_user_cmd(struct nvme_dev *dev, struct nvme_ns *ns,
 	return status;
 }
 
+static int nvme_subsys_reset(struct nvme_dev *dev)
+{
+	if (!dev->subsystem)
+		return -ENOTTY;
+
+	writel(0x4E564D65, &dev->bar->nssr); /* "NVMe" */
+	return 0;
+}
+
 static int nvme_ioctl(struct block_device *bdev, fmode_t mode, unsigned int cmd,
 							unsigned long arg)
 {
@@ -2932,6 +2941,8 @@ static long nvme_dev_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
 	case NVME_IOCTL_RESET:
 		dev_warn(dev->dev, "resetting controller\n");
 		return nvme_reset(dev);
+	case NVME_IOCTL_SUBSYS_RESET:
+		return nvme_subsys_reset(dev);
 	default:
 		return -ENOTTY;
 	}

include/linux/nvme.h

@@ -28,7 +28,7 @@ struct nvme_bar {
 	__u32			cc;	/* Controller Configuration */
 	__u32			rsvd1;	/* Reserved */
 	__u32			csts;	/* Controller Status */
-	__u32			rsvd2;	/* Reserved */
+	__u32			nssr;	/* Subsystem Reset */
 	__u32			aqa;	/* Admin Queue Attributes */
 	__u64			asq;	/* Admin SQ Base Address */
 	__u64			acq;	/* Admin CQ Base Address */

include/uapi/linux/nvme.h

@@ -584,5 +584,6 @@ struct nvme_passthru_cmd {
 #define NVME_IOCTL_SUBMIT_IO	_IOW('N', 0x42, struct nvme_user_io)
 #define NVME_IOCTL_IO_CMD	_IOWR('N', 0x43, struct nvme_passthru_cmd)
 #define NVME_IOCTL_RESET	_IO('N', 0x44)
+#define NVME_IOCTL_SUBSYS_RESET	_IO('N', 0x45)
 
 #endif /* _UAPI_LINUX_NVME_H */