[PATCH net-next 1/3] net: wwan: core: propagate modem control signals to port drivers

[Peter Hunt]

The WWAN character device emulates the TTY modem-control ioctls
(TIOCMGET/TIOCMSET/TIOCMBIC/TIOCMBIS) for AT and QCDM ports, but the
result is only stored in port->at_data.mdmbits and never reaches the port
driver. A driver therefore cannot act on the host raising or dropping
DTR/RTS, even though some modems depend on it (e.g. they withhold
unsolicited AT result codes until the host asserts DTR).

Add optional ->tiocmget/->tiocmset operations to struct wwan_port_ops and
call them from the AT/QCDM ioctl path. ->tiocmset is passed the resolved
TIOCM_* bitmask after BIC/BIS/SET has been applied; ->tiocmget, when
provided, refreshes the cached bits from the device. Drivers that do not
implement them keep the previous store-only behaviour.

Signed-off-by: Peter Hunt <peter.hunt@xxxxxxxxxxxx>
---
 drivers/net/wwan/wwan_core.c | 12 +++++++++++-
 include/linux/wwan.h         |  4 ++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wwan/wwan_core.c b/drivers/net/wwan/wwan_core.c
index ffbcf11e4e68..bf83eb5790fe 100644
--- a/drivers/net/wwan/wwan_core.c
+++ b/drivers/net/wwan/wwan_core.c
@@ -1018,7 +1018,15 @@ static long wwan_port_fops_at_ioctl(struct wwan_port *port, unsigned int cmd,
 #endif
 
 	case TIOCMGET:
-		ret = put_user(port->at_data.mdmbits, (int __user *)arg);
+		if (port->ops->tiocmget) {
+			ret = port->ops->tiocmget(port);
+			if (ret >= 0) {
+				port->at_data.mdmbits = ret;
+				ret = 0;
+			}
+		}
+		if (!ret)
+			ret = put_user(port->at_data.mdmbits, (int __user *)arg);
 		break;
 
 	case TIOCMSET:
@@ -1036,6 +1044,8 @@ static long wwan_port_fops_at_ioctl(struct wwan_port *port, unsigned int cmd,
 			port->at_data.mdmbits |= mdmbits;
 		else
 			port->at_data.mdmbits = mdmbits;
+		if (port->ops->tiocmset)
+			ret = port->ops->tiocmset(port, port->at_data.mdmbits);
 		break;
 	}
 
diff --git a/include/linux/wwan.h b/include/linux/wwan.h
index 1e0e2cb53579..bac02521e274 100644
--- a/include/linux/wwan.h
+++ b/include/linux/wwan.h
@@ -57,6 +57,8 @@ struct wwan_port;
  * @tx_blocking: Optional blocking routine that sends WWAN port protocol data
  *               to the device.
  * @tx_poll: Optional routine that sets additional TX poll flags.
+ * @tiocmget: Optional routine that reads the modem control lines.
+ * @tiocmset: Optional routine that sets the modem control lines.
  *
  * The wwan_port_ops structure contains a list of low-level operations
  * that control a WWAN port device. All functions are mandatory unless specified.
@@ -70,6 +72,8 @@ struct wwan_port_ops {
 	int (*tx_blocking)(struct wwan_port *port, struct sk_buff *skb);
 	__poll_t (*tx_poll)(struct wwan_port *port, struct file *filp,
 			    poll_table *wait);
+	int (*tiocmget)(struct wwan_port *port);
+	int (*tiocmset)(struct wwan_port *port, unsigned int mdmbits);
 };
 
 /** struct wwan_port_caps - The WWAN port capbilities
-- 
2.43.0