[PATCH 2/2] usb: gadget: f_uac2: allow changing interface name via configfs

[Yunhao Tian <t123yh.xyz@gmail.com>]

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>
---
 .../ABI/testing/configfs-usb-gadget-uac2      |  1 +
 Documentation/usb/gadget-testing.rst          |  1 +
 drivers/usb/gadget/function/f_uac2.c          | 46 ++++++++++++++++++-
 drivers/usb/gadget/function/u_uac2.h          |  2 +
 4 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/configfs-usb-gadget-uac2 b/Documentation/ABI/testing/configfs-usb-gadget-uac2
index cfd160ff8b56..3524f2b8446a 100644
--- a/Documentation/ABI/testing/configfs-usb-gadget-uac2
+++ b/Documentation/ABI/testing/configfs-usb-gadget-uac2
@@ -23,4 +23,5 @@ Description:
 		p_volume_min	playback volume control min value (in 1/256 dB)
 		p_volume_max	playback volume control max value (in 1/256 dB)
 		p_volume_res	playback volume control resolution (in 1/256 dB)
+		function_name	name of the interface
 		=========  ============================
diff --git a/Documentation/usb/gadget-testing.rst b/Documentation/usb/gadget-testing.rst
index 2cdb59411929..6df834f87bf2 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 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_uac2.c b/drivers/usb/gadget/function/f_uac2.c
index ef55b8bb5870..8f72ef361882 100644
--- a/drivers/usb/gadget/function/f_uac2.c
+++ b/drivers/usb/gadget/function/f_uac2.c
@@ -107,7 +107,7 @@ static char clksrc_in[8];
 static char clksrc_out[8];
 
 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 = clksrc_in,
 	[STR_CLKSRC_OUT].s = clksrc_out,
@@ -959,6 +959,8 @@ 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);
@@ -1834,6 +1836,42 @@ 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_ATTRIBUTE(u32, p_srate);
 UAC2_ATTRIBUTE(u32, p_ssize);
@@ -1855,6 +1893,7 @@ 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,
@@ -1879,6 +1918,8 @@ 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,
 };
 
@@ -1932,6 +1973,9 @@ static struct usb_function_instance *afunc_alloc_inst(void)
 
 	opts->req_number = UAC2_DEF_REQ_NUM;
 	opts->fb_max = UAC2_DEF_FB_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 a73b35774c44..4df23262db6e 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;
 };
-- 
2.25.1