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>

4 files changed, 49 insertions, 1 deletions

diff --git a/Documentation/ABI/testing/configfs-usb-gadget-uac1 b/Documentation/ABI/testing/configfs-usb-gadget-uac1
index 09725e273e9b..c4ba92f004c3 100644
--- a/Documentation/ABI/testing/configfs-usb-gadget-uac1
+++ b/Documentation/ABI/testing/configfs-usb-gadget-uac1
@@ -29,4 +29,5 @@ Description:
 					(in 1/256 dB)
 		req_number		the number of pre-allocated requests
 					for both capture and playback
+		function_name		name of the interface
 		=====================	=======================================
diff --git a/Documentation/usb/gadget-testing.rst b/Documentation/usb/gadget-testing.rst
index 046842b00c89..1792bd88f666 100644
--- a/Documentation/usb/gadget-testing.rst
+++ b/Documentation/usb/gadget-testing.rst
@@ -745,6 +745,7 @@ The uac2 function provides these attributes in its function directory:
 	p_volume_res     playback volume control resolution (in 1/256 dB)
 	req_number       the number of pre-allocated request for both capture
 	                 and playback
+	function_name    name of the interface
 	================ ====================================================
 
 The attributes have sane default values.
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;
 }
 
diff --git a/drivers/usb/gadget/function/u_uac1.h b/drivers/usb/gadget/function/u_uac1.h
index b6cd6171d306..f7a616760e31 100644
--- a/drivers/usb/gadget/function/u_uac1.h
+++ b/drivers/usb/gadget/function/u_uac1.h
@@ -52,6 +52,8 @@ struct f_uac1_opts {
 	int				req_number;
 	unsigned			bound:1;
 
+	char			function_name[32];
+
 	struct mutex			lock;
 	int				refcnt;
 };