linux-kernel - [PATCH 8/9] ALSA: usb-audio: Remove unneeded wmb() in mixer

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Message-Id: <20250526-dualsense-alsa-jack-v1-8-1a821463b632@collabora.com>
Date: Mon, 26 May 2025 17:07:47 +0300
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>
Cc: kernel@...labora.com, linux-sound@...r.kernel.org, 
 linux-kernel@...r.kernel.org
Subject: [PATCH 8/9] ALSA: usb-audio: Remove unneeded wmb() in mixer_quirks

Adding a memory barrier before wake_up() in
snd_usb_soundblaster_remote_complete() is supposed to ensure the write
to mixer->rc_code is visible in wait_event_interruptible() from
snd_usb_sbrc_hwdep_read().

However, this is not really necessary, since wake_up() is just a wrapper
over __wake_up() which already executes a full memory barrier before
accessing the state of the task to be waken up.

Drop the redundant call to wmb() and implicitly fix the checkpatch
complaint:

  WARNING: memory barrier without comment

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
---
 sound/usb/mixer_quirks.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/sound/usb/mixer_quirks.c b/sound/usb/mixer_quirks.c
index 783789cbcfe2901d7dcf30580fa19bac62898897..ffda3b8d42cc6b05ea26726616196a012cb6d1e4 100644
--- a/sound/usb/mixer_quirks.c
+++ b/sound/usb/mixer_quirks.c
@@ -212,7 +212,6 @@ static void snd_usb_soundblaster_remote_complete(struct urb *urb)
 	if (code == rc->mute_code)
 		snd_usb_mixer_notify_id(mixer, rc->mute_mixer_id);
 	mixer->rc_code = code;
-	wmb();
 	wake_up(&mixer->rc_waitq);
 }

-- 
2.49.0