usb: gadget: f_acm: make bInterfaceProtocol configurable

The bInterfaceProtocol is hardcoded to USB_CDC_ACM_PROTO_AT_V25TER. This
will lead to problems with ModemManger which will gladly try to probe
that port as a modem if the gadget also has a network function.
ModemManager will try to send AT commands to the ACM port. Make the
bInterfaceProtocol configurable. For this, track the number of instances
and only allow write to the property if there are no intances (yet).

This will also set bFunctionProtocol to the same value, see commit
5c8db070b448 ("USB: Change acm_iad_descriptor bFunctionProtocol to
USB_CDC_ACM_PROTO_AT_V25TER") for more details.

Signed-off-by: Michael Walle <mwalle@kernel.org>
Link: https://lore.kernel.org/r/20240825180446.3757073-1-mwalle@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/ABI/testing/configfs-usb-gadget-acm b/Documentation/ABI/testing/configfs-usb-gadget-acm
index d21092d75a0587ea8d7edbcd48a9af344388396d..25e68be9eb66124e608d5c477ee163fb757ff2da 100644 (file)
--- a/Documentation/ABI/testing/configfs-usb-gadget-acm
+++ b/Documentation/ABI/testing/configfs-usb-gadget-acm
@@ -6,3 +6,10 @@ Description:
                This item contains just one readonly attribute: port_num.
                It contains the port number of the /dev/ttyGS<n> device
                associated with acm function's instance "name".
+
+What:          /config/usb-gadget/gadget/functions/acm.name/protocol
+Date:          Aug 2024
+KernelVersion: 6.13
+Description:
+               Reported bInterfaceProtocol for the ACM device. For legacy
+               reasons, this defaults to 1 (USB_CDC_ACM_PROTO_AT_V25TER).

diff --git a/drivers/usb/gadget/function/f_acm.c b/drivers/usb/gadget/function/f_acm.c
index 724b2631f249b114291bb387c229e66b162afdf6..7061720b9732e4182b02ac3523d49c8e053176b7 100644 (file)
--- a/drivers/usb/gadget/function/f_acm.c
+++ b/drivers/usb/gadget/function/f_acm.c
@@ -41,6 +41,7 @@ struct f_acm {
        struct gserial                  port;
        u8                              ctrl_id, data_id;
        u8                              port_num;
+       u8                              bInterfaceProtocol;
 
        u8                              pending;
 
@@ -89,7 +90,7 @@ acm_iad_descriptor = {
        .bInterfaceCount =      2,      // control + data
        .bFunctionClass =       USB_CLASS_COMM,
        .bFunctionSubClass =    USB_CDC_SUBCLASS_ACM,
-       .bFunctionProtocol =    USB_CDC_ACM_PROTO_AT_V25TER,
+       /* .bFunctionProtocol = DYNAMIC */
        /* .iFunction =         DYNAMIC */
 };
 
@@ -101,7 +102,7 @@ static struct usb_interface_descriptor acm_control_interface_desc = {
        .bNumEndpoints =        1,
        .bInterfaceClass =      USB_CLASS_COMM,
        .bInterfaceSubClass =   USB_CDC_SUBCLASS_ACM,
-       .bInterfaceProtocol =   USB_CDC_ACM_PROTO_AT_V25TER,
+       /* .bInterfaceProtocol = DYNAMIC */
        /* .iInterface = DYNAMIC */
 };
 
@@ -663,6 +664,9 @@ acm_bind(struct usb_configuration *c, struct usb_function *f)
                goto fail;
        acm->notify = ep;
 
+       acm_iad_descriptor.bFunctionProtocol = acm->bInterfaceProtocol;
+       acm_control_interface_desc.bInterfaceProtocol = acm->bInterfaceProtocol;
+
        /* allocate notification */
        acm->notify_req = gs_alloc_req(ep,
                        sizeof(struct usb_cdc_notification) + 2,
@@ -719,8 +723,14 @@ static void acm_unbind(struct usb_configuration *c, struct usb_function *f)
 static void acm_free_func(struct usb_function *f)
 {
        struct f_acm            *acm = func_to_acm(f);
+       struct f_serial_opts    *opts;
+
+       opts = container_of(f->fi, struct f_serial_opts, func_inst);
 
        kfree(acm);
+       mutex_lock(&opts->lock);
+       opts->instances--;
+       mutex_unlock(&opts->lock);
 }
 
 static void acm_resume(struct usb_function *f)
@@ -761,7 +771,11 @@ static struct usb_function *acm_alloc_func(struct usb_function_instance *fi)
        acm->port.func.disable = acm_disable;
 
        opts = container_of(fi, struct f_serial_opts, func_inst);
+       mutex_lock(&opts->lock);
        acm->port_num = opts->port_num;
+       acm->bInterfaceProtocol = opts->protocol;
+       opts->instances++;
+       mutex_unlock(&opts->lock);
        acm->port.func.unbind = acm_unbind;
        acm->port.func.free_func = acm_free_func;
        acm->port.func.resume = acm_resume;
@@ -812,11 +826,42 @@ static ssize_t f_acm_port_num_show(struct config_item *item, char *page)
 
 CONFIGFS_ATTR_RO(f_acm_, port_num);
 
+static ssize_t f_acm_protocol_show(struct config_item *item, char *page)
+{
+       return sprintf(page, "%u\n", to_f_serial_opts(item)->protocol);
+}
+
+static ssize_t f_acm_protocol_store(struct config_item *item,
+               const char *page, size_t count)
+{
+       struct f_serial_opts *opts = to_f_serial_opts(item);
+       int ret;
+
+       mutex_lock(&opts->lock);
+
+       if (opts->instances) {
+               ret = -EBUSY;
+               goto out;
+       }
+
+       ret = kstrtou8(page, 0, &opts->protocol);
+       if (ret)
+               goto out;
+       ret = count;
+
+out:
+       mutex_unlock(&opts->lock);
+       return ret;
+}
+
+CONFIGFS_ATTR(f_acm_, protocol);
+
 static struct configfs_attribute *acm_attrs[] = {
 #ifdef CONFIG_U_SERIAL_CONSOLE
        &f_acm_attr_console,
 #endif
        &f_acm_attr_port_num,
+       &f_acm_attr_protocol,
        NULL,
 };
 
@@ -832,6 +877,7 @@ static void acm_free_instance(struct usb_function_instance *fi)
 
        opts = container_of(fi, struct f_serial_opts, func_inst);
        gserial_free_line(opts->port_num);
+       mutex_destroy(&opts->lock);
        kfree(opts);
 }
 
@@ -843,7 +889,9 @@ static struct usb_function_instance *acm_alloc_instance(void)
        opts = kzalloc(sizeof(*opts), GFP_KERNEL);
        if (!opts)
                return ERR_PTR(-ENOMEM);
+       opts->protocol = USB_CDC_ACM_PROTO_AT_V25TER;
        opts->func_inst.free_func_inst = acm_free_instance;
+       mutex_init(&opts->lock);
        ret = gserial_alloc_line(&opts->port_num);
        if (ret) {
                kfree(opts);

diff --git a/drivers/usb/gadget/function/u_serial.h b/drivers/usb/gadget/function/u_serial.h
index 901d99310bc48d083b2c129abc3bc99a3dc06399..e1274338ea61911f8da58d72155c89d7597e82c6 100644 (file)
--- a/drivers/usb/gadget/function/u_serial.h
+++ b/drivers/usb/gadget/function/u_serial.h
@@ -17,6 +17,10 @@
 struct f_serial_opts {
        struct usb_function_instance func_inst;
        u8 port_num;
+       u8 protocol;
+
+       struct mutex lock; /* protect instances */
+       int instances;
 };
 
 /*