linux-kernel - [PATCH] ALSA: usb-audio: Use atomic_try_cmpxchg in ep_state

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Date:   Wed, 13 Jul 2022 17:19:46 +0200
From:   Uros Bizjak <ubizjak@...il.com>
To:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Cc:     Uros Bizjak <ubizjak@...il.com>, Takashi Iwai <tiwai@...e.de>
Subject: [PATCH] ALSA: usb-audio: Use atomic_try_cmpxchg in ep_state_update

Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old in
ep_state_update. x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg (and related move instruction
in front of cmpxchg).

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Cc: Takashi Iwai <tiwai@...e.de>
---
 sound/usb/endpoint.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index f9c921683948..0d7b73bf7945 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -133,7 +133,7 @@ static inline bool ep_state_running(struct snd_usb_endpoint *ep)
 
 static inline bool ep_state_update(struct snd_usb_endpoint *ep, int old, int new)
 {
-	return atomic_cmpxchg(&ep->state, old, new) == old;
+	return atomic_try_cmpxchg(&ep->state, &old, new);
 }
 
 /**
-- 
2.35.3