[PATCH v3 2/3] soc: qcom: cmd-db: add reverse address-to-name lookup

RPMh resource addresses are opaque 32-bit values. While the slave ID
in bits [19:16] identifies the accelerator type (ARC/VRM/BCM), the
lower bits encode a resource index that is only meaningful when mapped
back to the human-readable resource name stored in the command DB
(e.g. 0x30000 -> cx.lvl).

Add cmd_db_read_name() to perform this reverse lookup by iterating
the command DB entries and matching on address. Unlike other exported
cmd-db APIs which go through cmd_db_get_header() (which calls
cmd_db_ready() internally), this function iterates cmd_db_header
directly for address matching, so it calls cmd_db_ready() itself.

For VRM resources,
which have up to 4 contiguous 4-byte-aligned addresses per resource,
the match uses VRM_ADDR() on bits [19:4] so that any sub-address
(enable, voltage, mode, headroom) resolves to the same resource name.

Also export CMD_DB_ID_SIZE so callers can size their name buffers
correctly without open-coding the magic constant 8.

Assisted-by: Claude:claude-sonnet-4-5
Reviewed-by: Dmitry Baryshkov <[email protected]>
Reviewed-by: Navya Malempati <[email protected]>
Signed-off-by: Maulik Shah <[email protected]>
---
 drivers/soc/qcom/cmd-db.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 include/soc/qcom/cmd-db.h |  5 +++++
 2 files changed, 50 insertions(+)

diff --git a/drivers/soc/qcom/cmd-db.c b/drivers/soc/qcom/cmd-db.c
index 117f810d5ca4..e1453b194aa3 100644
--- a/drivers/soc/qcom/cmd-db.c
+++ b/drivers/soc/qcom/cmd-db.c
@@ -287,6 +287,51 @@ const char *cmd_db_hw_type_str(u32 addr)
 }
 EXPORT_SYMBOL_GPL(cmd_db_hw_type_str);
 
+/**
+ * cmd_db_read_name() - Look up the resource name for a given RPMh address.
+ * @addr:  RPMh resource address to reverse-look up.
+ * @buf:   Output buffer to write the resource name into.
+ * @len:   Size of @buf; must be at least CMD_DB_ID_SIZE + 1.
+ *
+ * Iterates the command DB to find the entry whose address matches @addr.
+ * For VRM resources, which have up to 4 contiguous 4-byte-aligned addresses
+ * per resource, the match is performed on bits [19:4] so that any of the
+ * sub-addresses resolve to the same resource name.
+ *
+ * Return: 0 on success, -ENODEV if not found or DB not ready.
+ */
+int cmd_db_read_name(u32 addr, char *buf, size_t len)
+{
+	const struct rsc_hdr *rsc_hdr;
+	const struct entry_header *ent;
+	int ret, i, j;
+
+	ret = cmd_db_ready();
+	if (ret)
+		return ret;
+
+	for (i = 0; i < MAX_SLV_ID; i++) {
+		rsc_hdr = &cmd_db_header->header[i];
+		if (!rsc_hdr->slv_id)
+			break;
+
+		ent = rsc_to_entry_header(rsc_hdr);
+		for (j = 0; j < le16_to_cpu(rsc_hdr->cnt); j++, ent++) {
+			u32 ent_addr = le32_to_cpu(ent->addr);
+
+			if (cmd_db_match_resource_addr(ent_addr, addr)) {
+				snprintf(buf, len, "%.*s",
+					 (int)strnlen(ent->id, sizeof(ent->id)),
+					 ent->id);
+				return 0;
+			}
+		}
+	}
+
+	return -ENODEV;
+}
+EXPORT_SYMBOL_GPL(cmd_db_read_name);
+
 #ifdef CONFIG_DEBUG_FS
 static int cmd_db_debugfs_dump(struct seq_file *seq, void *p)
 {
diff --git a/include/soc/qcom/cmd-db.h b/include/soc/qcom/cmd-db.h
index 34adc04eac94..d03d64f3407d 100644
--- a/include/soc/qcom/cmd-db.h
+++ b/include/soc/qcom/cmd-db.h
@@ -9,6 +9,8 @@
 
 #include <linux/err.h>
 
+#define CMD_DB_ID_SIZE		8
+
 enum cmd_db_hw_type {
 	CMD_DB_HW_INVALID = 0,
 	CMD_DB_HW_MIN     = 3,
@@ -31,6 +33,7 @@ enum cmd_db_hw_type cmd_db_read_slave_id(const char *resource_id);
 int cmd_db_ready(void);
 
 const char *cmd_db_hw_type_str(u32 addr);
+int cmd_db_read_name(u32 addr, char *buf, size_t len);
 #else
 static inline u32 cmd_db_read_addr(const char *resource_id)
 { return 0; }
@@ -49,5 +52,7 @@ static inline int cmd_db_ready(void)
 
 static inline const char *cmd_db_hw_type_str(u32 addr)
 { return "unknown"; }
+static inline int cmd_db_read_name(u32 addr, char *buf, size_t len)
+{ return -ENODEV; }
 #endif /* CONFIG_QCOM_COMMAND_DB */
 #endif /* __QCOM_COMMAND_DB_H__ */

-- 
2.43.0