lightnvm: Inherit mdts from the parent nvme device

Current lightnvm and pblk implementation does not care about NVMe max
data transfer size, which can be smaller than 64*K=256K. There are
existing NVMe controllers which NVMe max data transfer size is lower
that 256K (for example 128K, which happens for existing NVMe
controllers which are NVMe spec compliant). Such a controllers are not
able to handle command which contains 64 PPAs, since the the size of
DMAed buffer will be above the capabilities of such a controller.
Signed-off-by: Igor Konopko <igor.j.konopko@intel.com>
Reviewed-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Reviewed-by: Javier González <javier@javigon.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/lightnvm/core.c

@@ -325,6 +325,7 @@ static int nvm_create_tgt(struct nvm_dev *dev, struct nvm_ioctl_create *create)
 	struct nvm_target *t;
 	struct nvm_tgt_dev *tgt_dev;
 	void *targetdata;
+	unsigned int mdts;
 	int ret;
 
 	switch (create->conf.type) {
@@ -412,8 +413,12 @@ static int nvm_create_tgt(struct nvm_dev *dev, struct nvm_ioctl_create *create)
 	tdisk->private_data = targetdata;
 	tqueue->queuedata = targetdata;
 
-	blk_queue_max_hw_sectors(tqueue,
-			(dev->geo.csecs >> 9) * NVM_MAX_VLBA);
+	mdts = (dev->geo.csecs >> 9) * NVM_MAX_VLBA;
+	if (dev->geo.mdts) {
+		mdts = min_t(u32, dev->geo.mdts,
+				(dev->geo.csecs >> 9) * NVM_MAX_VLBA);
+	}
+	blk_queue_max_hw_sectors(tqueue, mdts);
 
 	set_capacity(tdisk, tt->capacity(targetdata));
 	add_disk(tdisk);

drivers/nvme/host/lightnvm.c

@@ -977,6 +977,7 @@ int nvme_nvm_register(struct nvme_ns *ns, char *disk_name, int node)
 	geo->csecs = 1 << ns->lba_shift;
 	geo->sos = ns->ms;
 	geo->ext = ns->ext;
+	geo->mdts = ns->ctrl->max_hw_sectors;
 
 	dev->q = q;
 	memcpy(dev->name, disk_name, DISK_NAME_LEN);

include/linux/lightnvm.h

@@ -358,6 +358,7 @@ struct nvm_geo {
 	u16	csecs;		/* sector size */
 	u16	sos;		/* out-of-band area size */
 	bool	ext;		/* metadata in extended data buffer */
+	u32	mdts;		/* Max data transfer size*/
 
 	/* device write constrains */
 	u32	ws_min;		/* minimum write size */