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

Takashi Iwai
2026-03-05T12:06:19Z

On Thu, 05 Mar 2026 07:13:32 +0100,
Terry Junge wrote:
>
>
>
> 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, that's good to know!

Rong, could you submit the cleanup patch? I already applied your
series, so write on top of sound.git tree for-next branch.

I'll work on a clean up of the other existing code in USB-audio, too.

Takashi