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Message-ID: <20251209164006.143219-1-victor.krawiec@arturia.com>
Date: Tue, 9 Dec 2025 17:40:06 +0100
From: Victor Krawiec <victor.krawiec@...uria.com>
To: gregkh@...uxfoundation.org
Cc: tiwai@...e.de,
corbet@....net,
jilliandonahue58@...il.com,
selvarasu.g@...sung.com,
jkeeping@...usicbrands.com,
linux-kernel@...r.kernel.org,
linux-usb@...r.kernel.org,
linux-doc@...r.kernel.org,
linux-api@...r.kernel.org,
Victor Krawiec <victor.krawiec@...uria.com>
Subject: [PATCH v2] usb: gadget: f_midi: allow customizing the USB MIDI interface string through configfs
When using f_midi from configfs the USB MIDI interface string is hardcoded
to 'MIDI function'.
This USB string descriptor is used by some third-party OS or software to
display the name of the MIDI device
Since we add an additional string option a new macro block was created to
factorize declarations
Signed-off-by: Victor Krawiec <victor.krawiec@...uria.com>
---
V1 -> V2:
- Add documentation
- Cleanup unnecessary *_allocated boolean as requested in review
.../ABI/testing/configfs-usb-gadget-midi | 17 +--
Documentation/usb/gadget-testing.rst | 17 +--
drivers/usb/gadget/function/f_midi.c | 110 ++++++++++--------
drivers/usb/gadget/function/u_midi.h | 2 +-
4 files changed, 78 insertions(+), 68 deletions(-)
diff --git a/Documentation/ABI/testing/configfs-usb-gadget-midi b/Documentation/ABI/testing/configfs-usb-gadget-midi
index 07389cddd51a..d6bd67bb91fc 100644
--- a/Documentation/ABI/testing/configfs-usb-gadget-midi
+++ b/Documentation/ABI/testing/configfs-usb-gadget-midi
@@ -4,11 +4,12 @@ KernelVersion: 3.19
Description:
The attributes:
- ========== ====================================
- index index value for the USB MIDI adapter
- id ID string for the USB MIDI adapter
- buflen MIDI buffer length
- qlen USB read request queue length
- in_ports number of MIDI input ports
- out_ports number of MIDI output ports
- ========== ====================================
+ ================ ====================================
+ index index value for the USB MIDI adapter
+ id ID string for the USB MIDI adapter
+ buflen MIDI buffer length
+ qlen USB read request queue length
+ in_ports number of MIDI input ports
+ out_ports number of MIDI output ports
+ interface_string USB AudioControl interface string
+ ================ ====================================
diff --git a/Documentation/usb/gadget-testing.rst b/Documentation/usb/gadget-testing.rst
index 5f90af1fb573..01a128d664cb 100644
--- a/Documentation/usb/gadget-testing.rst
+++ b/Documentation/usb/gadget-testing.rst
@@ -368,14 +368,15 @@ Function-specific configfs interface
The function name to use when creating the function directory is "midi".
The MIDI function provides these attributes in its function directory:
- =============== ====================================
- buflen MIDI buffer length
- id ID string for the USB MIDI adapter
- in_ports number of MIDI input ports
- index index value for the USB MIDI adapter
- out_ports number of MIDI output ports
- qlen USB read request queue length
- =============== ====================================
+ ================ ====================================
+ buflen MIDI buffer length
+ id ID string for the USB MIDI adapter
+ in_ports number of MIDI input ports
+ index index value for the USB MIDI adapter
+ out_ports number of MIDI output ports
+ qlen USB read request queue length
+ interface_string USB AudioControl interface string
+ ================ ====================================
Testing the MIDI function
-------------------------
diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
index da82598fcef8..ad679a6ecac1 100644
--- a/drivers/usb/gadget/function/f_midi.c
+++ b/drivers/usb/gadget/function/f_midi.c
@@ -875,6 +875,7 @@ static int f_midi_bind(struct usb_configuration *c, struct usb_function *f)
struct usb_composite_dev *cdev = c->cdev;
struct f_midi *midi = func_to_midi(f);
struct usb_string *us;
+ struct f_midi_opts *opts;
int status, n, jack = 1, i = 0, endpoint_descriptor_index = 0;
midi->gadget = cdev->gadget;
@@ -883,6 +884,10 @@ static int f_midi_bind(struct usb_configuration *c, struct usb_function *f)
if (status < 0)
goto fail_register;
+ opts = container_of(f->fi, struct f_midi_opts, func_inst);
+ if (opts->interface_string)
+ midi_string_defs[STRING_FUNC_IDX].s = opts->interface_string;
+
/* maybe allocate device-global string ID */
us = usb_gstrings_attach(c->cdev, midi_strings,
ARRAY_SIZE(midi_string_defs));
@@ -1178,59 +1183,60 @@ end: \
\
CONFIGFS_ATTR(f_midi_opts_, name);
+#define F_MIDI_OPT_STRING(name) \
+static ssize_t f_midi_opts_##name##_show(struct config_item *item, char *page) \
+{ \
+ struct f_midi_opts *opts = to_f_midi_opts(item); \
+ ssize_t result; \
+ \
+ mutex_lock(&opts->lock); \
+ if (opts->name) { \
+ result = strscpy(page, opts->name, PAGE_SIZE); \
+ } else { \
+ page[0] = 0; \
+ result = 0; \
+ } \
+ \
+ mutex_unlock(&opts->lock); \
+ \
+ return result; \
+} \
+ \
+static ssize_t f_midi_opts_##name##_store(struct config_item *item, \
+ const char *page, size_t len) \
+{ \
+ struct f_midi_opts *opts = to_f_midi_opts(item); \
+ int ret; \
+ char *c; \
+ \
+ mutex_lock(&opts->lock); \
+ if (opts->refcnt > 1) { \
+ ret = -EBUSY; \
+ goto end; \
+ } \
+ \
+ c = kstrndup(page, len, GFP_KERNEL); \
+ if (!c) { \
+ ret = -ENOMEM; \
+ goto end; \
+ } \
+ kfree(opts->name); \
+ opts->name = c; \
+ ret = len; \
+end: \
+ mutex_unlock(&opts->lock); \
+ return ret; \
+} \
+ \
+CONFIGFS_ATTR(f_midi_opts_, name)
+
F_MIDI_OPT_SIGNED(index, true, SNDRV_CARDS);
F_MIDI_OPT(buflen, false, 0);
F_MIDI_OPT(qlen, false, 0);
F_MIDI_OPT(in_ports, true, MAX_PORTS);
F_MIDI_OPT(out_ports, true, MAX_PORTS);
-
-static ssize_t f_midi_opts_id_show(struct config_item *item, char *page)
-{
- struct f_midi_opts *opts = to_f_midi_opts(item);
- ssize_t result;
-
- mutex_lock(&opts->lock);
- if (opts->id) {
- result = strscpy(page, opts->id, PAGE_SIZE);
- } else {
- page[0] = 0;
- result = 0;
- }
-
- mutex_unlock(&opts->lock);
-
- return result;
-}
-
-static ssize_t f_midi_opts_id_store(struct config_item *item,
- const char *page, size_t len)
-{
- struct f_midi_opts *opts = to_f_midi_opts(item);
- int ret;
- char *c;
-
- mutex_lock(&opts->lock);
- if (opts->refcnt > 1) {
- ret = -EBUSY;
- goto end;
- }
-
- c = kstrndup(page, len, GFP_KERNEL);
- if (!c) {
- ret = -ENOMEM;
- goto end;
- }
- if (opts->id_allocated)
- kfree(opts->id);
- opts->id = c;
- opts->id_allocated = true;
- ret = len;
-end:
- mutex_unlock(&opts->lock);
- return ret;
-}
-
-CONFIGFS_ATTR(f_midi_opts_, id);
+F_MIDI_OPT_STRING(id);
+F_MIDI_OPT_STRING(interface_string);
static struct configfs_attribute *midi_attrs[] = {
&f_midi_opts_attr_index,
@@ -1239,6 +1245,7 @@ static struct configfs_attribute *midi_attrs[] = {
&f_midi_opts_attr_in_ports,
&f_midi_opts_attr_out_ports,
&f_midi_opts_attr_id,
+ &f_midi_opts_attr_interface_string,
NULL,
};
@@ -1262,8 +1269,8 @@ static void f_midi_free_inst(struct usb_function_instance *f)
mutex_unlock(&opts->lock);
if (free) {
- if (opts->id_allocated)
- kfree(opts->id);
+ kfree(opts->id);
+ kfree(opts->interface_string);
kfree(opts);
}
}
@@ -1279,7 +1286,8 @@ static struct usb_function_instance *f_midi_alloc_inst(void)
mutex_init(&opts->lock);
opts->func_inst.free_func_inst = f_midi_free_inst;
opts->index = SNDRV_DEFAULT_IDX1;
- opts->id = SNDRV_DEFAULT_STR1;
+ opts->id = NULL;
+ opts->interface_string = NULL;
opts->buflen = 512;
opts->qlen = 32;
opts->in_ports = 1;
diff --git a/drivers/usb/gadget/function/u_midi.h b/drivers/usb/gadget/function/u_midi.h
index 2e400b495cb8..41cb8aa73f09 100644
--- a/drivers/usb/gadget/function/u_midi.h
+++ b/drivers/usb/gadget/function/u_midi.h
@@ -19,7 +19,7 @@ struct f_midi_opts {
struct usb_function_instance func_inst;
int index;
char *id;
- bool id_allocated;
+ char *interface_string;
unsigned int in_ports;
unsigned int out_ports;
unsigned int buflen;
base-commit: 67a454e6b1c604555c04501c77b7fedc5d98a779
--
2.43.0
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