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

Terry Junge
2026-03-05T06:21:26Z

On 3/1/26 1:37 PM, Rong Zhang wrote:
> 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)

Hi Rong,

This function is not necessary.
Both the manufacturer and product strings can be found in struct usb_device.

If the device has a manufacturer string then chip->dev->manufacturer points to it.
Otherwise chip->dev->manufacturer is null.

Likewise, chip->dev->product points to the product string if there is one, else null.

> +{
> + 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);
> + }

No need to get the strings as they can be found at chip->dev->manufacturer and chip->dev->product
if the device declared them.

> +
> + 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;

Examples and intent:

DEVICE_STRING_FLG(vid, pid, "acme", "alpha", flags) // match vid, pid, "acme", and "alpha" strings
DEVICE_STRING_FLG(vid, pid, "acme", "", flags) // match vid, pid, "acme", and device has no product string
DEVICE_STRING_FLG(vid, pid, "acme", 0, flags) // match vid, pid, "acme", and any product string
DEVICE_STRING_FLG(vid, pid, 0, "alpha", flags) // match vid, pid, any manufacturer string, and "alpha"
DEVICE_STRING_FLG(vid, pid, "", "alpha", flags) // match vid, pid, no manufacturer string, and "alpha"
DEVICE_STRING_FLG(vid, pid, "", "", flags) // match vid, pid, no manufacturer, and no product strings

This test would change to something like

if (p->usb_string_match->manufacturer &&
strcmp(p->usb_string_match->manufacturer, chip->dev->manufacturer ? chip->dev->manufacturer : ""))
continue;

> +
> + if (p->usb_string_match->product &&
> + strcmp(p->usb_string_match->product, product))
> + continue;

Same here but product instead of manufacturer.

Thanks,
Terry

> +
> +apply:
> snd_usb_apply_flag_dbg("builtin table", chip, p->flags);
> chip->quirk_flags |= p->flags;
> return;