[PATCH 4/9] ALSA: usb-audio: Support string-descriptor-based quirk table entry

Rong Zhang
2026-03-01T21:38:02Z

Some quirky devices do not have a unique VID/PID. Matching them using
DEVICE_FLG() or VENDOR_FLG() may result in conflicts.

Add two new macros DEVICE_STRING_FLG() and VENDOR_STRING_FLG() to match
USB string descriptors (manufacturer and/or product) in addition to VID
and/or PID, so that we can deconflict these devices safely.

No functional change intended.

Signed-off-by: Rong Zhang <i@rong.moe>
---
sound/usb/quirks.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 82 insertions(+)

diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index c6a78efbcaa30..495dd46ce515c 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -2,8 +2,10 @@
/*
*/

+#include <linux/build_bug.h>
#include <linux/init.h>
#include <linux/slab.h>
+#include <linux/string.h>
#include <linux/usb.h>
#include <linux/usb/audio.h>
#include <linux/usb/midi.h>
@@ -2135,16 +2137,39 @@ void snd_usb_audioformat_attributes_quirk(struct snd_usb_audio *chip,
/*
* driver behavior quirk flags
*/
+struct usb_string_match {
+ const char *manufacturer;
+ const char *product;
+};
+
struct usb_audio_quirk_flags_table {
u32 id;
u32 flags;
+ const struct usb_string_match *usb_string_match;
};

#define DEVICE_FLG(vid, pid, _flags) \
{ .id = USB_ID(vid, pid), .flags = (_flags) }
#define VENDOR_FLG(vid, _flags) DEVICE_FLG(vid, 0, _flags)

+/* Use as a last resort if using DEVICE_FLG() is prone to VID/PID conflicts. */
+#define DEVICE_STRING_FLG(vid, pid, _manufacturer, _product, _flags) \
+{ \
+ .id = USB_ID(vid, pid), \
+ .usb_string_match = &(const struct usb_string_match) { \
+ .manufacturer = _manufacturer, \
+ .product = _product, \
+ }, \
+ .flags = (_flags), \
+}
+
+/* Use as a last resort if using VENDOR_FLG() is prone to VID conflicts. */
+#define VENDOR_STRING_FLG(vid, _manufacturer, _flags) \
+ DEVICE_STRING_FLG(vid, 0, _manufacturer, NULL, _flags)
+
static const struct usb_audio_quirk_flags_table quirk_flags_table[] = {
+ /* Device and string descriptor matches */
+
/* Device matches */
DEVICE_FLG(0x001f, 0x0b21, /* AB13X USB Audio */
QUIRK_FLAG_FORCE_IFACE_RESET | QUIRK_FLAG_IFACE_DELAY),
@@ -2414,6 +2439,8 @@ static const struct usb_audio_quirk_flags_table quirk_flags_table[] = {
DEVICE_FLG(0x534d, 0x2109, /* MacroSilicon MS2109 */
QUIRK_FLAG_ALIGN_TRANSFER),

+ /* Vendor and string descriptor matches */
+
/* Vendor matches */
VENDOR_FLG(0x045e, /* MS Lifecam */
QUIRK_FLAG_GET_SAMPLE_RATE),
@@ -2558,14 +2585,69 @@ void snd_usb_apply_flag_dbg(const char *reason,
}
}

+#define USB_STRING_SIZE 128
+
+static inline int snd_usb_get_strings(struct snd_usb_audio *chip,
+ char *manufacturer, char *product)
+{
+ int ret;
+
+ if (manufacturer) {
+ ret = usb_string(chip->dev, chip->dev->descriptor.iManufacturer,
+ manufacturer, USB_STRING_SIZE);
+ if (ret < 0) {
+ usb_audio_warn(chip, "failed to get manufacturer string: %d\n", ret);
+ return ret;
+ }
+ }
+
+ if (product) {
+ ret = usb_string(chip->dev, chip->dev->descriptor.iProduct,
+ product, USB_STRING_SIZE);
+ if (ret < 0) {
+ usb_audio_warn(chip, "failed to get product string: %d\n", ret);
+ return ret;
+ }
+ }
+
+ return 1; /* ok */
+}
+
void snd_usb_init_quirk_flags_table(struct snd_usb_audio *chip)
{
const struct usb_audio_quirk_flags_table *p;
+ char manufacturer[USB_STRING_SIZE];
+ char product[USB_STRING_SIZE];
+ int got_usb_strings = 0; /* <0: error, 0: pending, >0: ok */

for (p = quirk_flags_table; p->id; p++) {
if (chip->usb_id == p->id ||
(!USB_ID_PRODUCT(p->id) &&
USB_ID_VENDOR(chip->usb_id) == USB_ID_VENDOR(p->id))) {
+ if (!p->usb_string_match)
+ goto apply; /* DEVICE_FLG or VENDOR_FLG */
+
+ /* DEVICE_STRING_FLG or VENDOR_STRING_FLG */
+ if (!got_usb_strings) {
+ got_usb_strings = snd_usb_get_strings(chip,
+ p->usb_string_match->manufacturer ? manufacturer : NULL,
+ p->usb_string_match->product ? product : NULL);
+ }
+
+ BUILD_BUG_ON(!got_usb_strings);
+
+ if (got_usb_strings < 0)
+ continue;
+
+ if (p->usb_string_match->manufacturer &&
+ strcmp(p->usb_string_match->manufacturer, manufacturer))
+ continue;
+
+ if (p->usb_string_match->product &&
+ strcmp(p->usb_string_match->product, product))
+ continue;
+
+apply:
snd_usb_apply_flag_dbg("builtin table", chip, p->flags);
chip->quirk_flags |= p->flags;
return;
--
2.51.0