linux-kernel - [PATCH 5.15 31/76] ALSA: usb-audio: Properly refcounting clock rate

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Message-ID: <20240313164223.615640-32-sashal@kernel.org>
Date: Wed, 13 Mar 2024 12:41:38 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Takashi Iwai <tiwai@...e.de>,
	Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 31/76] ALSA: usb-audio: Properly refcounting clock rate

From: Takashi Iwai <tiwai@...e.de>

[ Upstream commit 9a737e7f8b371e97eb649904276407cee2c9cf30 ]

We fixed the bug introduced by the patch for managing the shared
clocks at the commit 809f44a0cc5a ("ALSA: usb-audio: Clear fixed clock
rate at closing EP"), but it was merely a workaround.  By this change,
the clock reference rate is cleared at each EP close, hence the still
remaining EP may need a re-setup of rate unnecessarily.

This patch introduces the proper refcounting for the clock reference
object so that the clock setup is done only when needed.

Fixes: 809f44a0cc5a ("ALSA: usb-audio: Clear fixed clock rate at closing EP")
Fixes: c11117b634f4 ("ALSA: usb-audio: Refcount multiple accesses on the single clock")
Link: https://lore.kernel.org/r/20220920181126.4912-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Stable-dep-of: 7822baa844a8 ("ALSA: usb-audio: add quirk for RODE NT-USB+")
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 sound/usb/endpoint.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index 32a9e016665c8..2d3f814d067b5 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -39,6 +39,7 @@ struct snd_usb_iface_ref {
 struct snd_usb_clock_ref {
 	unsigned char clock;
 	atomic_t locked;
+	int opened;
 	int rate;
 	bool need_setup;
 	struct list_head list;
@@ -810,6 +811,7 @@ snd_usb_endpoint_open(struct snd_usb_audio *chip,
 				ep = NULL;
 				goto unlock;
 			}
+			ep->clock_ref->opened++;
 		}
 
 		ep->cur_audiofmt = fp;
@@ -934,8 +936,10 @@ void snd_usb_endpoint_close(struct snd_usb_audio *chip,
 		endpoint_set_interface(chip, ep, false);
 
 	if (!--ep->opened) {
-		if (ep->clock_ref && !atomic_read(&ep->clock_ref->locked))
-			ep->clock_ref->rate = 0;
+		if (ep->clock_ref) {
+			if (!--ep->clock_ref->opened)
+				ep->clock_ref->rate = 0;
+		}
 		ep->iface = 0;
 		ep->altsetting = 0;
 		ep->cur_audiofmt = NULL;
@@ -1656,8 +1660,7 @@ void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep, bool keep_pending)
 			WRITE_ONCE(ep->sync_source->sync_sink, NULL);
 		stop_urbs(ep, false, keep_pending);
 		if (ep->clock_ref)
-			if (!atomic_dec_return(&ep->clock_ref->locked))
-				ep->clock_ref->rate = 0;
+			atomic_dec(&ep->clock_ref->locked);
 	}
 }
 
-- 
2.43.0