[PATCH v5 5/8] nvme: add from0based() helper

[Caleb Sander Mateos <csander@purestorage.com>]

The NVMe specifications are big fans of "0's based"/"0-based" fields for
encoding values that must be positive. The encoded value is 1 less than
the value it represents. nvmet already provides a helper to0based() for
encoding 0's based values, so add a corresponding helper to decode these
fields on the host side.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
---
 drivers/nvme/host/nvme.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 9971045dbc05..ccd5e05dac98 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -760,10 +760,16 @@ static inline sector_t nvme_lba_to_sect(struct nvme_ns_head *head, u64 lba)
 static inline u32 nvme_bytes_to_numd(size_t len)
 {
 	return (len >> 2) - 1;
 }
 
+/* Decode a 2-byte "0's based"/"0-based" field */
+static inline u32 from0based(__le16 value)
+{
+	return (u32)le16_to_cpu(value) + 1;
+}
+
 static inline bool nvme_is_ana_error(u16 status)
 {
 	switch (status & NVME_SCT_SC_MASK) {
 	case NVME_SC_ANA_TRANSITION:
 	case NVME_SC_ANA_INACCESSIBLE:
-- 
2.45.2