[PATCH v5 3/7] mfd: nct6694: Introduce transport abstraction with function pointers

[a0282524688]

From: Ming Yu <a0282524688@xxxxxxxxx>

Add `read_msg` and `write_msg` function pointers to `struct nct6694`
and provide static inline helpers for sub-devices. The USB-specific
I/O functions are made static and assigned during probe.

This decouples sub-device drivers from the underlying USB implementation,
paving the way for alternative transport interfaces (e.g., HIF) in the
future without modifying client drivers.

Signed-off-by: Ming Yu <a0282524688@xxxxxxxxx>
---
Changes in v5:
- Split from the monolithic v4 patch to follow the single logical change principle.

 drivers/mfd/nct6694.c       | 12 ++++++++----
 include/linux/mfd/nct6694.h | 22 ++++++++++++++++++++--
 2 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/drivers/mfd/nct6694.c b/drivers/mfd/nct6694.c
index 58c1cbcbe3f2..b88863a0b70f 100644
--- a/drivers/mfd/nct6694.c
+++ b/drivers/mfd/nct6694.c
@@ -115,7 +115,9 @@ static int nct6694_response_err_handling(struct nct6694 *nct6694, unsigned char
  *
  * Return: Negative value on error or 0 on success.
  */
-int nct6694_read_msg(struct nct6694 *nct6694, const struct nct6694_cmd_header *cmd_hd, void *buf)
+static int nct6694_read_msg(struct nct6694 *nct6694,
+			    const struct nct6694_cmd_header *cmd_hd,
+			    void *buf)
 {
 	struct nct6694_usb_data *udata = nct6694->priv;
 	union nct6694_usb_msg *msg = udata->usb_msg;
@@ -153,7 +155,6 @@ int nct6694_read_msg(struct nct6694 *nct6694, const struct nct6694_cmd_header *c
 
 	return nct6694_response_err_handling(nct6694, msg->response_header.sts);
 }
-EXPORT_SYMBOL_GPL(nct6694_read_msg);
 
 /**
  * nct6694_write_msg() - Write message to NCT6694 device
@@ -166,7 +167,9 @@ EXPORT_SYMBOL_GPL(nct6694_read_msg);
  *
  * Return: Negative value on error or 0 on success.
  */
-int nct6694_write_msg(struct nct6694 *nct6694, const struct nct6694_cmd_header *cmd_hd, void *buf)
+static int nct6694_write_msg(struct nct6694 *nct6694,
+			     const struct nct6694_cmd_header *cmd_hd,
+			     void *buf)
 {
 	struct nct6694_usb_data *udata = nct6694->priv;
 	union nct6694_usb_msg *msg = udata->usb_msg;
@@ -210,7 +213,6 @@ int nct6694_write_msg(struct nct6694 *nct6694, const struct nct6694_cmd_header *
 
 	return nct6694_response_err_handling(nct6694, msg->response_header.sts);
 }
-EXPORT_SYMBOL_GPL(nct6694_write_msg);
 
 static void usb_int_callback(struct urb *urb)
 {
@@ -327,6 +329,8 @@ static int nct6694_usb_probe(struct usb_interface *iface,
 	udata->udev = udev;
 
 	nct6694->priv = udata;
+	nct6694->read_msg = nct6694_read_msg;
+	nct6694->write_msg = nct6694_write_msg;
 
 	nct6694->domain = irq_domain_create_simple(NULL, NCT6694_NR_IRQS, 0,
 						   &nct6694_irq_domain_ops,
diff --git a/include/linux/mfd/nct6694.h b/include/linux/mfd/nct6694.h
index 3f5dd53f38de..3079c74110aa 100644
--- a/include/linux/mfd/nct6694.h
+++ b/include/linux/mfd/nct6694.h
@@ -92,9 +92,27 @@ struct nct6694 {
 	spinlock_t irq_lock;
 	unsigned int irq_enable;
 	void *priv;
+
+	int (*read_msg)(struct nct6694 *nct6694,
+			const struct nct6694_cmd_header *cmd_hd,
+			void *buf);
+	int (*write_msg)(struct nct6694 *nct6694,
+			 const struct nct6694_cmd_header *cmd_hd,
+			 void *buf);
 };
 
-int nct6694_read_msg(struct nct6694 *nct6694, const struct nct6694_cmd_header *cmd_hd, void *buf);
-int nct6694_write_msg(struct nct6694 *nct6694, const struct nct6694_cmd_header *cmd_hd, void *buf);
+static inline int nct6694_read_msg(struct nct6694 *nct6694,
+				   const struct nct6694_cmd_header *cmd_hd,
+				   void *buf)
+{
+	return nct6694->read_msg(nct6694, cmd_hd, buf);
+}
+
+static inline int nct6694_write_msg(struct nct6694 *nct6694,
+				    const struct nct6694_cmd_header *cmd_hd,
+				    void *buf)
+{
+	return nct6694->write_msg(nct6694, cmd_hd, buf);
+}
 
 #endif
-- 
2.34.1