usb: gadget: f_uac2: 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 "Source/Sink" just as before.

Signed-off-by: Yunhao Tian <t123yh.xyz@gmail.com>
Link: https://lore.kernel.org/r/20220122112446.1415547-2-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-uac2 b/Documentation/ABI/testing/configfs-usb-gadget-uac2
index 9d2f59ab9701..4c6bf63fcb22 100644
--- a/Documentation/ABI/testing/configfs-usb-gadget-uac2
+++ b/Documentation/ABI/testing/configfs-usb-gadget-uac2
@@ -32,4 +32,5 @@ 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 1792bd88f666..6e8fdfaf19e7 100644
--- a/Documentation/usb/gadget-testing.rst
+++ b/Documentation/usb/gadget-testing.rst
@@ -934,6 +934,7 @@ The uac1 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 requests 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_uac2.c b/drivers/usb/gadget/function/f_uac2.c
index 3e6339439b88..d874e0d34188 100644
--- a/drivers/usb/gadget/function/f_uac2.c
+++ b/drivers/usb/gadget/function/f_uac2.c
@@ -107,7 +107,7 @@ enum {
 };
 
 static struct usb_string strings_fn[] = {
-	[STR_ASSOC].s = "Source/Sink",
+	/* [STR_ASSOC].s = DYNAMIC, */
 	[STR_IF_CTRL].s = "Topology Control",
 	[STR_CLKSRC_IN].s = "Input Clock",
 	[STR_CLKSRC_OUT].s = "Output Clock",
@@ -984,6 +984,8 @@ afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
 	if (ret)
 		return ret;
 
+	strings_fn[STR_ASSOC].s = uac2_opts->function_name;
+
 	us = usb_gstrings_attach(cdev, fn_strings, ARRAY_SIZE(strings_fn));
 	if (IS_ERR(us))
 		return PTR_ERR(us);
@@ -1963,6 +1965,42 @@ end:									\
 									\
 CONFIGFS_ATTR(f_uac2_opts_, name)
 
+#define UAC2_ATTRIBUTE_STRING(name)					\
+static ssize_t f_uac2_opts_##name##_show(struct config_item *item,	\
+					 char *page)			\
+{									\
+	struct f_uac2_opts *opts = to_f_uac2_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_uac2_opts_##name##_store(struct config_item *item,	\
+					  const char *page, size_t len)	\
+{									\
+	struct f_uac2_opts *opts = to_f_uac2_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_uac2_opts_, name)
+
 UAC2_ATTRIBUTE(u32, p_chmask);
 UAC2_RATE_ATTRIBUTE(p_srate);
 UAC2_ATTRIBUTE(u32, p_ssize);
@@ -1984,6 +2022,7 @@ UAC2_ATTRIBUTE(s16, c_volume_min);
 UAC2_ATTRIBUTE(s16, c_volume_max);
 UAC2_ATTRIBUTE(s16, c_volume_res);
 UAC2_ATTRIBUTE(u32, fb_max);
+UAC2_ATTRIBUTE_STRING(function_name);
 
 static struct configfs_attribute *f_uac2_attrs[] = {
 	&f_uac2_opts_attr_p_chmask,
@@ -2008,6 +2047,8 @@ static struct configfs_attribute *f_uac2_attrs[] = {
 	&f_uac2_opts_attr_c_volume_max,
 	&f_uac2_opts_attr_c_volume_res,
 
+	&f_uac2_opts_attr_function_name,
+
 	NULL,
 };
 
@@ -2061,6 +2102,9 @@ static struct usb_function_instance *afunc_alloc_inst(void)
 
 	opts->req_number = UAC2_DEF_REQ_NUM;
 	opts->fb_max = FBACK_FAST_MAX;
+
+	snprintf(opts->function_name, sizeof(opts->function_name), "Source/Sink");
+
 	return &opts->func_inst;
 }
 
diff --git a/drivers/usb/gadget/function/u_uac2.h b/drivers/usb/gadget/function/u_uac2.h
index 6bfcf6d0e863..ed96c7c853e4 100644
--- a/drivers/usb/gadget/function/u_uac2.h
+++ b/drivers/usb/gadget/function/u_uac2.h
@@ -59,6 +59,8 @@ struct f_uac2_opts {
 	int				fb_max;
 	bool			bound;
 
+	char			function_name[32];
+
 	struct mutex			lock;
 	int				refcnt;
 };