ALSA: usb-audio: Rewrite registration quirk handling

A slight refactoring of the registration quirk code.  Now it uses the
table lookup for easy additions in future.  Also the return type was
changed to bool, and got a few more comments.

Link: https://lore.kernel.org/r/20200325103322.2508-2-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/card.c

@@ -665,7 +665,7 @@ static int usb_audio_probe(struct usb_interface *intf,
 	/* we are allowed to call snd_card_register() many times, but first
 	 * check to see if a device needs to skip it or do anything special
 	 */
-	if (snd_usb_registration_quirk(chip, ifnum) == 0) {
+	if (!snd_usb_registration_quirk(chip, ifnum)) {
 		err = snd_card_register(chip->card);
 		if (err < 0)
 			goto __error;

sound/usb/quirks.c

@@ -1809,16 +1809,36 @@ void snd_usb_audioformat_attributes_quirk(struct snd_usb_audio *chip,
 	}
 }
 
-int snd_usb_registration_quirk(struct snd_usb_audio *chip,
-			       int iface)
+/*
+ * registration quirk:
+ * the registration is skipped if a device matches with the given ID,
+ * unless the interface reaches to the defined one.  This is for delaying
+ * the registration until the last known interface, so that the card and
+ * devices appear at the same time.
+ */
+
+struct registration_quirk {
+	unsigned int usb_id;	/* composed via USB_ID() */
+	unsigned int interface;	/* the interface to trigger register */
+};
+
+#define REG_QUIRK_ENTRY(vendor, product, iface) \
+	{ .usb_id = USB_ID(vendor, product), .interface = (iface) }
+
+static const struct registration_quirk registration_quirks[] = {
+	REG_QUIRK_ENTRY(0x0951, 0x16d8, 2),	/* Kingston HyperX AMP */
+	{ 0 }					/* terminator */
+};
+
+/* return true if skipping registration */
+bool snd_usb_registration_quirk(struct snd_usb_audio *chip, int iface)
 {
-	switch (chip->usb_id) {
-	case USB_ID(0x0951, 0x16d8): /* Kingston HyperX AMP */
-		/* Register only when we reach interface 2 so that streams can
-		 * merge correctly into PCMs from interface 0
-		 */
-		return (iface != 2);
-	}
+	const struct registration_quirk *q;
+
+	for (q = registration_quirks; q->usb_id; q++)
+		if (chip->usb_id == q->usb_id)
+			return iface != q->interface;
+
 	/* Register as normal */
-	return 0;
+	return false;
 }

sound/usb/quirks.h

@@ -51,7 +51,6 @@ void snd_usb_audioformat_attributes_quirk(struct snd_usb_audio *chip,
 					  struct audioformat *fp,
 					  int stream);
 
-int snd_usb_registration_quirk(struct snd_usb_audio *chip,
-			       int iface);
+bool snd_usb_registration_quirk(struct snd_usb_audio *chip, int iface);
 
 #endif /* __USBAUDIO_QUIRKS_H */