nvme: add from0based() helper

calebsander · keithbusch · commit b465046c8cca · 2026-03-27T07:35:04.000-07:00
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 &lt;hch@lst.de&gt;
Signed-off-by: Caleb Sander Mateos &lt;csander@purestorage.com&gt;
Signed-off-by: Keith Busch &lt;kbusch@kernel.org&gt;
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
@@ -762,6 +762,12 @@ 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) {

Original file line number	Diff line number	Diff line change
`@@ -762,6 +762,12 @@ static inline u32 nvme_bytes_to_numd(size_t len)`
`762`	`762`	`return (len >> 2) - 1;`
`763`	`763`	`}`
`764`	`764`
	`765`	`+/* Decode a 2-byte "0's based"/"0-based" field */`
	`766`	`+static inline u32 from0based(__le16 value)`
	`767`	`+{`
	`768`	`+ return (u32)le16_to_cpu(value) + 1;`
	`769`	`+}`
	`770`	`+`
`765`	`771`	`static inline bool nvme_is_ana_error(u16 status)`
`766`	`772`	`{`
`767`	`773`	`switch (status & NVME_SCT_SC_MASK) {`