[PATCH 1/2] usb: gadget: f_uac1: allow changing interface name via configfs

[Yunhao Tian]

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@xxxxxxxxx>
---
 .../ABI/testing/configfs-usb-gadget-uac1      |  1 +
 Documentation/usb/gadget-testing.rst          |  1 +
 drivers/usb/gadget/function/f_uac1.c          | 46 ++++++++++++++++++-
 drivers/usb/gadget/function/u_uac1.h          |  2 +
 4 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/configfs-usb-gadget-uac1 b/Documentation/ABI/testing/configfs-usb-gadget-uac1
index dd647d44d975..ca66623a7700 100644
--- a/Documentation/ABI/testing/configfs-usb-gadget-uac1
+++ b/Documentation/ABI/testing/configfs-usb-gadget-uac1
@@ -23,4 +23,5 @@ Description:
 		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
 		==========	===================================
diff --git a/Documentation/usb/gadget-testing.rst b/Documentation/usb/gadget-testing.rst
index c18113077889..2cdb59411929 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 5b3502df4e13..b1f9f4d36abb 100644
--- a/drivers/usb/gadget/function/f_uac1.c
+++ b/drivers/usb/gadget/function/f_uac1.c
@@ -303,7 +303,7 @@ 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",
@@ -1129,6 +1129,8 @@ 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);
@@ -1413,6 +1415,42 @@ 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_ATTRIBUTE(u32, c_srate);
 UAC1_ATTRIBUTE(u32, c_ssize);
@@ -1432,6 +1470,7 @@ 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,
@@ -1453,6 +1492,8 @@ static struct configfs_attribute *f_uac1_attrs[] = {
 	&f_uac1_opts_attr_c_volume_min,
 	&f_uac1_opts_attr_c_volume_max,
 	&f_uac1_opts_attr_c_volume_res,
+
+	&f_uac1_opts_attr_function_name,
 
 	NULL,
 };
@@ -1505,6 +1546,9 @@ 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 589fae861141..c94b6da16b68 100644
--- a/drivers/usb/gadget/function/u_uac1.h
+++ b/drivers/usb/gadget/function/u_uac1.h
@@ -51,6 +51,8 @@ struct f_uac1_opts {
 	int				req_number;
 	unsigned			bound:1;
 
+	char			function_name[32];
+
 	struct mutex			lock;
 	int				refcnt;
 };
-- 
2.25.1