Maximum Data Transfer Size (MDTS) field indicates the maximum
data transfer size between the host and the controller. The
host should not submit a command that exceeds this transfer
size. The value is in units of the minimum memory page size
and is reported as a power of two (2^n).
The spec also says: a value of 0h indicates no restrictions
on transfer size. On the real NVMe card this is normally not
0 due to hardware restrictions, but with QEMU emulated NVMe
device it reports as 0. In nvme_blk_read/write() below we
have the following algorithm for maximum number of logic
blocks per transfer:
u16 lbas = 1 << (dev->max_transfer_shift - ns->lba_shift);
dev->max_transfer_shift being 0 will for sure cause lbas to
overflow. Let's use 20. With this fix, the NVMe driver works
on QEMU emulated NVMe device.
Signed-off-by: Bin Meng <bmeng...@gmail.com>
---
drivers/nvme/nvme.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/drivers/nvme/nvme.c b/drivers/nvme/nvme.c
index bac253a..151fe92 100644
--- a/drivers/nvme/nvme.c
+++ b/drivers/nvme/nvme.c
@@ -563,6 +563,27 @@ static int nvme_get_info_from_identify(struct nvme_dev
*dev)
memcpy(dev->firmware_rev, ctrl->fr, sizeof(ctrl->fr));
if (ctrl->mdts)
dev->max_transfer_shift = (ctrl->mdts + shift);
+ else {
+ /*
+ * Maximum Data Transfer Size (MDTS) field indicates the maximum
+ * data transfer size between the host and the controller. The
+ * host should not submit a command that exceeds this transfer
+ * size. The value is in units of the minimum memory page size
+ * and is reported as a power of two (2^n).
+ *
+ * The spec also says: a value of 0h indicates no restrictions
+ * on transfer size. But in nvme_blk_read/write() below we have
+ * the following algorithm for maximum number of logic blocks
+ * per transfer:
+ *
+ * u16 lbas = 1 << (dev->max_transfer_shift - ns->lba_shift);
+ *
+ * In order for lbas not to overflow, the maximum number is 15
+ * which means dev->max_transfer_shift = 15 + 9 (ns->lba_shift).
+ * Let's use 20 which provides 1MB size.
+ */
+ dev->max_transfer_shift = 20;
+ }
/* Apply quirk stuff */
dm_pci_read_config16(dev->pdev, PCI_VENDOR_ID, &vendor);
--
2.9.2
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