From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1A0832D5408 for ; Sat, 30 May 2026 21:38:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780177125; cv=none; b=mM+ohSeDDL54xRm0JdbPpFWOgT3QK0l4QpIR36g9Nnx5/QH0m1hMTQ4kVj4GHUnt/sBGkhDI/FSdvuCpNIESAoh4JGBeEqLcbfz51L0Ki3lhiCVrY+IIIs7XD7bRbpp0WPspPw5mx83Cwa088x0rHfLF4ljHeXUhd3Mhw4aXj9s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780177125; c=relaxed/simple; bh=xigOy34CuWt1yPhZAaxndGtKiUaWVQglbZX2Qnj822M=; h=From:To:Subject:Date:Message-ID:In-Reply-To:References: Content-Type:MIME-Version; b=Y0/PkrsX8GG/x1hntPvWy4ahxOPS+FOduFXteRfYwfMoyqbZMbDoBJl/JsGmUhaErNoR5NmDt6iwOn/R1QKcN6a7hMXGHHVl8jmecIVoaKyswOotC7DcrXntzA+AxfwWB7IN7RfWTrsTo4t8GLneucYCFHezwi1HBSCU1orRCs0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VEFKFrm7; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="VEFKFrm7" Received: by smtp.kernel.org (Postfix) with ESMTPS id A79E1C19425 for ; Sat, 30 May 2026 21:38:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1780177124; bh=xigOy34CuWt1yPhZAaxndGtKiUaWVQglbZX2Qnj822M=; h=From:To:Subject:Date:In-Reply-To:References:From; b=VEFKFrm7v5RRpKdWL2nvaZzD2WZbCN1bG0hzqs63x/MEUiPPtZSdA2fR+ftqgKkDf Y/k/8kc7ZQUGblWw7B06GdJQo6c1UiNdO7w5jnAxdBLGHFcxlmwCbDJ3yjlBEbF/MX 0oKQyTe574jKvkb4XHGMFzDgJyXVcDcs5+VvJa8KJhNbuE96ChlGwVHZv5ojXPuQX/ cHfN4prIlIsrJzD+HqcNI4D/B1eFUwnpgdFHFfag9de9nvYlOilkMD0eGnzr03m3Qx VGfuhzEWj+ii29fUr1MVTHlStUzCks9mrdFP+ygMgLNa0uw50nsmfd2yAOnLZ3hw3P g3lMbTkOOLWig== Received: by aws-us-west-2-korg-bugzilla-1.web.codeaurora.org (Postfix, from userid 48) id 88094C3279F; Sat, 30 May 2026 21:38:44 +0000 (UTC) From: bugzilla-daemon@kernel.org To: linux-bluetooth@vger.kernel.org Subject: [Bug 221598] Bluetooth: btusb/btrtl RTL8821C 0bda:c821 HFP/mSBC microphone stutters with bursty SCO RX delivery Date: Sat, 30 May 2026 21:38:44 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Drivers X-Bugzilla-Component: Bluetooth X-Bugzilla-Version: 2.5 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: apocarteres@gmail.com X-Bugzilla-Status: NEW X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: linux-bluetooth@vger.kernel.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugzilla.kernel.org/ Auto-Submitted: auto-generated Precedence: bulk X-Mailing-List: linux-bluetooth@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 https://bugzilla.kernel.org/show_bug.cgi?id=3D221598 --- Comment #7 from Alexander Paderin (apocarteres@gmail.com) --- Additional update after isolating user-space HCI traffic: I found a strong practical mitigation/confounder: stopping/removing Blueman significantly improves the HFP/mSBC microphone quality on this machine. Before this test, Blueman UI processes were running: - `blueman-manager` - `blueman-applet` - `blueman-tray` The bad traces with Blueman running contained frequent HCI control traffic, especially: - `Read RSSI` (`0x1405`) - `Read Transmit Power Level` (`0x0c2d`) After stopping/removing Blueman, the same headset/machine produced much cle= aner captures. The subjective microphone stutter also became noticeably better. Summary of RX mSBC/H2 continuity results: | run | extra HCI polling | RX H2 markers | bad seq | bad seq/k | bad dist | bad dist/k | |---|---:|---:|---:|---:|---:|---:| | old control | yes | 3486 | 21 | 6.02 | 23 | 6.60 | | no-Blueman control 1 | no | 4301 | 6 | 1.39 | 15 | 3.49 | | no-Blueman control 2 | no | 4312 | 6 | 1.39 | 6 | 1.39 | | bad noisy watch-only run | yes | 3949 | 454 | 114.97 | 425 | 107.62 | | bad noisy raw-open repeat | yes | 4812 | 453 | 94.14 | 385 | 80.01 | TX remained clean in all runs (`bad_sequence=3D0`, `bad_distance=3D0`). Important caveat: I then tried to reproduce the issue without Blueman by injecting the same polling manually after eSCO setup. The stress script sen= t 25 pairs of: - `Read RSSI` (`0x1405`) - `Read Transmit Power Level` (`0x0c2d`) That did not reproduce the catastrophic bad runs: | run | polling | RX H2 markers | bad seq | bad seq/k | bad dist | bad dist= /k | |---|---:|---:|---:|---:|---:|---:| | no-Blueman control 2 | no | 4312 | 6 | 1.39 | 6 | 1.39 | | artificial HCI polling stress | 25 RSSI + 25 TX-power reads | 3778 | 16 | 4.24 | 13 | 3.44 | So `Read RSSI` / `Read Transmit Power Level` alone is not proven to be the direct root cause. The stronger conclusion is: - Removing Blueman is a real practical mitigation on this RTL8821C/0bda:c821 system. - Extra user-space HCI management/control traffic is a strong confounder and can correlate with much worse RX mSBC continuity. - The underlying failure still appears to be RX-only H2/mSBC continuity los= s: host TX stays clean, eSCO setup parameters remain normal, and RX still has = some breaks even in the clean no-Blueman baseline. Relevant local captures/reports: - `captures/sco-control-test-20260531-002158.snoop` - `captures/sco-control-test-20260531-002431.snoop` - `captures/hci-poll-stress-test-20260531-003222.snoop` - `reports/control-no-blueman-20260531-002158-findings.md` - `reports/control-no-blueman-repeat-20260531-002431-findings.md` - `reports/hci-poll-stress-20260531-003222-findings.md` --=20 You may reply to this email to add a comment. You are receiving this mail because: You are the assignee for the bug.=