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

[Takashi Iwai]

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@xxxxxxxx>
> > ---
> >  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