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nvme: Handle zero Maximum Data Transfer Size (MDTS)

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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.cn@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
This commit is contained in:
Bin Meng 2017-08-03 02:31:02 -07:00 committed by Tom Rini
parent f81d83d534
commit beb5f52139
1 changed files with 21 additions and 0 deletions
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21
drivers/nvme/nvme.c
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@ -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);