ALSA: scarlett2: Default mixer driver to enabled

Early versions of this mixer driver did not work on all hardware, so
out of caution the driver was disabled by default and had to be
explicitly enabled with device_setup=1.

Since commit 764fa6e6 ("ALSA: usb-audio: scarlett2: Fix device
hang with ehci-pci") no more problems of this nature have been
reported. Therefore, enable the driver by default but provide a new
device_setup option to disable the driver in case that is needed.

- device_setup value of 0 now means "enable" rather than "disable".
- device_setup value of 1 is now ignored.
- device_setup value of 4 now means "disable".
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/89600a35b40307f2766578ad1ca2f21801286b58.1694705811.git.g@b4.vuSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett_gen2.c

@@ -141,12 +141,12 @@
 
 #include "mixer_scarlett_gen2.h"
 
-/* device_setup value to enable */
-#define SCARLETT2_ENABLE 0x01
-
 /* device_setup value to allow turning MSD mode back on */
 #define SCARLETT2_MSD_ENABLE 0x02
 
+/* device_setup value to disable this mixer driver */
+#define SCARLETT2_DISABLE 0x04
+
 /* some gui mixers can't handle negative ctl values */
 #define SCARLETT2_VOLUME_BIAS 127
 
@@ -4172,19 +4172,20 @@ int snd_scarlett_gen2_init(struct usb_mixer_interface *mixer)
 	if (!mixer->protocol)
 		return 0;
 
-	if (!(chip->setup & SCARLETT2_ENABLE)) {
+	if (chip->setup & SCARLETT2_DISABLE) {
 		usb_audio_info(chip,
-			"Focusrite Scarlett Gen 2/3 Mixer Driver disabled; "
-			"use options snd_usb_audio vid=0x%04x pid=0x%04x "
-			"device_setup=1 to enable and report any issues "
-			"to g@b4.vu",
+			"Focusrite Scarlett Gen 2/3 Mixer Driver disabled "
+			"by modprobe options (snd_usb_audio "
+			"vid=0x%04x pid=0x%04x device_setup=%d)\n",
 			USB_ID_VENDOR(chip->usb_id),
-			USB_ID_PRODUCT(chip->usb_id));
+			USB_ID_PRODUCT(chip->usb_id),
+			SCARLETT2_DISABLE);
 		return 0;
 	}
 
 	usb_audio_info(chip,
-		"Focusrite Scarlett Gen 2/3 Mixer Driver enabled pid=0x%04x",
+		"Focusrite Scarlett Gen 2/3 Mixer Driver enabled (pid=0x%04x); "
+		"report any issues to g@b4.vu",
 		USB_ID_PRODUCT(chip->usb_id));
 
 	err = snd_scarlett_gen2_controls_create(mixer);