usb: gadget: f_uac1: allow changing interface name via configfs

This adds "function_name" configfs entry to change string value
of the iInterface field. This field will be shown in Windows' audio
settings panel, so being able to change it is useful. It will default
to "AC Interface" just as before if unchanged.

Signed-off-by: Yunhao Tian <t123yh.xyz@gmail.com>
Link: https://lore.kernel.org/r/20220122112446.1415547-1-t123yh.xyz@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 45 insertions, 1 deletions

diff --git a/drivers/usb/gadget/function/f_uac1.c b/drivers/usb/gadget/function/f_uac1.c
index 1484e5c231d3..6f0e1d803dc2 100644
--- a/drivers/usb/gadget/function/f_uac1.c
+++ b/drivers/usb/gadget/function/f_uac1.c
@@ -309,7 +309,7 @@ enum {
 };
 
 static struct usb_string strings_uac1[] = {
-	[STR_AC_IF].s = "AC Interface",
+	/* [STR_AC_IF].s = DYNAMIC, */
 	[STR_USB_OUT_IT].s = "Playback Input terminal",
 	[STR_USB_OUT_IT_CH_NAMES].s = "Playback Channels",
 	[STR_IO_OUT_OT].s = "Playback Output terminal",
@@ -1192,6 +1192,8 @@ static int f_audio_bind(struct usb_configuration *c, struct usb_function *f)
 
 	audio_opts = container_of(f->fi, struct f_uac1_opts, func_inst);
 
+	strings_uac1[STR_AC_IF].s = audio_opts->function_name;
+
 	us = usb_gstrings_attach(cdev, uac1_strings, ARRAY_SIZE(strings_uac1));
 	if (IS_ERR(us))
 		return PTR_ERR(us);
@@ -1551,6 +1553,42 @@ end:									\
 									\
 CONFIGFS_ATTR(f_uac1_opts_, name)
 
+#define UAC1_ATTRIBUTE_STRING(name)					\
+static ssize_t f_uac1_opts_##name##_show(struct config_item *item,	\
+					 char *page)			\
+{									\
+	struct f_uac1_opts *opts = to_f_uac1_opts(item);		\
+	int result;							\
+									\
+	mutex_lock(&opts->lock);					\
+	result = snprintf(page, sizeof(opts->name), "%s", opts->name);	\
+	mutex_unlock(&opts->lock);					\
+									\
+	return result;							\
+}									\
+									\
+static ssize_t f_uac1_opts_##name##_store(struct config_item *item,	\
+					  const char *page, size_t len)	\
+{									\
+	struct f_uac1_opts *opts = to_f_uac1_opts(item);		\
+	int ret = 0;							\
+									\
+	mutex_lock(&opts->lock);					\
+	if (opts->refcnt) {						\
+		ret = -EBUSY;						\
+		goto end;						\
+	}								\
+									\
+	ret = snprintf(opts->name, min(sizeof(opts->name), len),	\
+			"%s", page);					\
+									\
+end:									\
+	mutex_unlock(&opts->lock);					\
+	return ret;							\
+}									\
+									\
+CONFIGFS_ATTR(f_uac1_opts_, name)
+
 UAC1_ATTRIBUTE(u32, c_chmask);
 UAC1_RATE_ATTRIBUTE(c_srate);
 UAC1_ATTRIBUTE(u32, c_ssize);
@@ -1570,6 +1608,7 @@ UAC1_ATTRIBUTE(bool, c_volume_present);
 UAC1_ATTRIBUTE(s16, c_volume_min);
 UAC1_ATTRIBUTE(s16, c_volume_max);
 UAC1_ATTRIBUTE(s16, c_volume_res);
+UAC1_ATTRIBUTE_STRING(function_name);
 
 static struct configfs_attribute *f_uac1_attrs[] = {
 	&f_uac1_opts_attr_c_chmask,
@@ -1592,6 +1631,8 @@ static struct configfs_attribute *f_uac1_attrs[] = {
 	&f_uac1_opts_attr_c_volume_max,
 	&f_uac1_opts_attr_c_volume_res,
 
+	&f_uac1_opts_attr_function_name,
+
 	NULL,
 };
 
@@ -1643,6 +1684,9 @@ static struct usb_function_instance *f_audio_alloc_inst(void)
 	opts->c_volume_res = UAC1_DEF_RES_DB;
 
 	opts->req_number = UAC1_DEF_REQ_NUM;
+
+	snprintf(opts->function_name, sizeof(opts->function_name), "AC Interface");
+
 	return &opts->func_inst;
 }