[PATCH v6 9/9] tty: n_gsm: add restart flag to extended ioctl config

["D. Starke" <daniel.starke@siemens.com>]

From: Daniel Starke <daniel.starke@siemens.com>

Currently, changing the parameters of the n_gsm mux gives no direct control
to the user whether this should trigger a mux reset or not. The decision is
solely made by the driver based on the assumption which parameter changes
are compatible or not. Therefore, the user has no means to perform an
automatic mux reset after parameter configuration for non-conflicting
changes.

Add the parameter 'flags' to 'gsm_config_ext' to force a mux reset after
ioctl setting regardless of whether the changes made require this or not
by setting this to 'GSM_FL_RESTART'. This is done similar to
'GSM_FL_RESTART' in gsm_dlci_config.flags.

Note that 'GSM_FL_RESTART' is currently the only allowed flag to allow
additions here.

Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
---
 drivers/tty/n_gsm.c         | 23 +++++++++++++++++++++++
 include/uapi/linux/gsmmux.h |  5 ++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

v5 -> v6:
No changes. This was previously patch 10/10. Patch 9/10 has been removed.

Link: https://lore.kernel.org/all/2023081644-stiffness-division-215b@gregkh/
Link: https://lore.kernel.org/all/20230517155704.5701-10-daniel.starke@siemens.com/

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 47905803f8f9..8ecc7b138c05 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -3422,6 +3422,7 @@ static void gsm_copy_config_ext_values(struct gsm_mux *gsm,
 
 static int gsm_config_ext(struct gsm_mux *gsm, struct gsm_config_ext *ce)
 {
+	bool need_restart = false;
 	unsigned int i;
 
 	/*
@@ -3431,6 +3432,20 @@ static int gsm_config_ext(struct gsm_mux *gsm, struct gsm_config_ext *ce)
 	for (i = 0; i < ARRAY_SIZE(ce->reserved); i++)
 		if (ce->reserved[i])
 			return -EINVAL;
+	if (ce->flags & ~GSM_FL_RESTART)
+		return -EINVAL;
+
+	/* Requires care */
+	if (ce->flags & GSM_FL_RESTART)
+		need_restart = true;
+
+	/*
+	 * Close down what is needed, restart and initiate the new
+	 * configuration. On the first time there is no DLCI[0]
+	 * and closing or cleaning up is not necessary.
+	 */
+	if (need_restart)
+		gsm_cleanup_mux(gsm, true);
 
 	/*
 	 * Setup the new configuration values
@@ -3438,6 +3453,14 @@ static int gsm_config_ext(struct gsm_mux *gsm, struct gsm_config_ext *ce)
 	gsm->wait_config = ce->wait_config ? true : false;
 	gsm->keep_alive = ce->keep_alive;
 
+	if (gsm->dead) {
+		int ret = gsm_activate_mux(gsm);
+		if (ret)
+			return ret;
+		if (gsm->initiator)
+			gsm_dlci_begin_open(gsm->dlci[0]);
+	}
+
 	return 0;
 }
 
diff --git a/include/uapi/linux/gsmmux.h b/include/uapi/linux/gsmmux.h
index 3bd6f03a8293..4c878d84dbda 100644
--- a/include/uapi/linux/gsmmux.h
+++ b/include/uapi/linux/gsmmux.h
@@ -11,6 +11,7 @@
  * flags definition for n_gsm
  *
  * Used by:
+ * struct gsm_config_ext.flags
  * struct gsm_dlci_config.flags
  */
 /* Forces a DLCI reset if set. Otherwise, a DLCI reset is only done if
@@ -98,12 +99,14 @@ struct gsm_netconfig {
  *
  * @keep_alive:  Control channel keep-alive in 1/100th of a second (0 to disable).
  * @wait_config: Wait for DLCI config before opening virtual link?
+ * @flags:       Mux specific flags.
  * @reserved:    For future use, must be initialized to zero.
  */
 struct gsm_config_ext {
 	__u32 keep_alive;
 	__u32 wait_config;
-	__u32 reserved[6];
+	__u32 flags;
+	__u32 reserved[5];
 };
 
 #define GSMIOC_GETCONF_EXT	_IOR('G', 5, struct gsm_config_ext)
-- 
2.34.1