[PATCH v2 2/9] tty: n_gsm: add restart parameter to DLC specific ioctl config

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

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

Currently, changing the parameters of a DLCI gives no direct control to the
user whether this should trigger a channel 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 channel reset after parameter configuration for non-conflicting
changes.

Add the parameter 'restart' to 'gsm_dlci_config' to force a channel reset
after ioctl setting regardless of whether the changes made require this or
not.

Note that the parameter is limited to the values 0 and 1 to allow future
additions here.

Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
---
 drivers/tty/n_gsm.c         | 4 ++++
 include/uapi/linux/gsmmux.h | 3 ++-
 2 files changed, 6 insertions(+), 1 deletion(-)

v1 -> v2:
Changed wording as remarked in the review.

Link: https://lore.kernel.org/all/AS4PR10MB5895BA5B2ECFFF74DDBAB571E0919@AS4PR10MB5895.EURPRD10.PROD.OUTLOOK.COM/

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index c42c8b89fd46..eb21ca583642 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2531,6 +2531,8 @@ static int gsm_dlci_config(struct gsm_dlci *dlci, struct gsm_dlci_config *dc, in
 		return -EINVAL;
 	if (dc->k > 7)
 		return -EINVAL;
+	if (dc->restart > 1)   /* allow future extensions */
+		return -EINVAL;
 
 	/*
 	 * See what is needed for reconfiguration
@@ -2545,6 +2547,8 @@ static int gsm_dlci_config(struct gsm_dlci *dlci, struct gsm_dlci_config *dc, in
 	/* Requires care */
 	if (dc->priority != dlci->prio)
 		need_restart = true;
+	if (dc->restart)
+		need_restart = true;
 
 	if ((open && gsm->wait_config) || need_restart)
 		need_open = true;
diff --git a/include/uapi/linux/gsmmux.h b/include/uapi/linux/gsmmux.h
index eb67884e5f38..33ee7b857c52 100644
--- a/include/uapi/linux/gsmmux.h
+++ b/include/uapi/linux/gsmmux.h
@@ -58,7 +58,8 @@ struct gsm_dlci_config {
 	__u32 priority;		/* Priority (0 for default value) */
 	__u32 i;		/* Frame type (1 = UIH, 2 = UI) */
 	__u32 k;		/* Window size (0 for default value) */
-	__u32 reserved[8];	/* For future use, must be initialized to zero */
+	__u32 restart;		/* Force DLCI channel reset? */
+	__u32 reserved[7];	/* For future use, must be initialized to zero */
 };
 
 #define GSMIOC_GETCONF_DLCI	_IOWR('G', 7, struct gsm_dlci_config)
-- 
2.34.1