[PATCH] ALSA: usb-audio: Optimize TEAC clock quirk

[Takashi Iwai]

Maris found out that the quirk for TEAC devices to work around the
clock setup is needed to apply only when the base clock is changed,
e.g. from 48000-based clocks (48000, 96000, 192000, 384000) to
44100-based clocks (44100, 88200, 176400, 352800), or vice versa,
while switching to another clock with the same base clock doesn't need
the (forcible) interface setup.

This patch implements the optimization for the TEAC clock quirk to
avoid the unnecessary interface re-setup.

Fixes: 5ce0b06ae5e6 ("ALSA: usb-audio: Workaround for clock setup on TEAC devices")
Reported-by: Maris Abele <maris7abele at gmail.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/usb/clock.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/sound/usb/clock.c b/sound/usb/clock.c
index 3c435d379306..db429320599e 100644
--- a/sound/usb/clock.c
+++ b/sound/usb/clock.c
@@ -573,10 +573,14 @@ static int set_sample_rate_v2v3(struct snd_usb_audio *chip,
 	}
 
 	/* FIXME - TEAC devices require the immediate interface setup */
-	if (rate != prev_rate && USB_ID_VENDOR(chip->usb_id) == 0x0644) {
-		usb_set_interface(chip->dev, fmt->iface, fmt->altsetting);
-		if (chip->quirk_flags & QUIRK_FLAG_IFACE_DELAY)
-			msleep(50);
+	if (USB_ID_VENDOR(chip->usb_id) == 0x0644) {
+		bool cur_base_48k = (rate % 48000 == 0);
+		bool prev_base_48k = (prev_rate % 48000 == 0);
+		if (cur_base_48k != prev_base_48k) {
+			usb_set_interface(chip->dev, fmt->iface, fmt->altsetting);
+			if (chip->quirk_flags & QUIRK_FLAG_IFACE_DELAY)
+				msleep(50);
+		}
 	}
 
 validation:
-- 
2.35.3