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 1E196548EE for ; Sat, 30 May 2026 22:12:47 +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=1780179168; cv=none; b=ssfKgnowBBwtMCt7rJrxRJ2dmNNbmJmb5BFdijVIZfsYJf38CAUMMBt0QaZwhsJqNxy3s1uRsxDXKQt5ZU8QF7+tPpBvXkLpV9T6JCsUKYJS8Kht571Rvm2FmPuTOePoz7uHzan5EgS13qbjAS4kA8Glk2MbHKLuCGJfrHwgU+s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780179168; c=relaxed/simple; bh=f2DS6uheccaYtPYnC3HtpIMsSEXPjjgORtBj84+HPWk=; h=From:To:Subject:Date:Message-ID:In-Reply-To:References: Content-Type:MIME-Version; b=GmWF8/FJ/rXH6hQAhZdk20sFeogqaAU1L1ZsMQ2cHAXMPy/Yl4EFN5ib15E4u/FancsNuMzpv6rc7hDoY3OqT2xK7h7qwCM93LaEqxuQkjBkS8UWHPKxu1XmX3LlWoQncJz7hYpCW1CeWPnjbAK62GfPY8D8XAi/XhefxWDDsEo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VtvEnVWi; 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="VtvEnVWi" Received: by smtp.kernel.org (Postfix) with ESMTPS id 9778DC19425 for ; Sat, 30 May 2026 22:12:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1780179167; bh=f2DS6uheccaYtPYnC3HtpIMsSEXPjjgORtBj84+HPWk=; h=From:To:Subject:Date:In-Reply-To:References:From; b=VtvEnVWi32h9XYiq4T4oIYJ+kZDVHn/Fm2zdeN9eCBcZ5um06gQav6+Tnchja2EPv XdI/zDwfEmGZEKJS611DEcUDCrEHqZw5jO17tXwCWYdj6t+mUn9Cx1Ory2ZmUoSTjS A32UdVBdeSN9YFgQuTXp0aShTlsLJMaaJXez4PDH1ZFrLeSm7KpnJnivynYksexwnE tr6YvOoG+YDSECw548bMntJwLCcaYg/NfsnJEZfgFgKETf5UxoppPwd1hoe2vmTVER nOnoWmDF2B4vCnfUU9DghrkqkVVt7Pnq4krQjdhVnt/VDEI0Q3kwFBU481Gl+I6k8d ue4maVpnGz6gw== Received: by aws-us-west-2-korg-bugzilla-1.web.codeaurora.org (Postfix, from userid 48) id 774D1C3279F; Sat, 30 May 2026 22:12:47 +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 22:12:47 +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 #8 from Alexander Paderin (apocarteres@gmail.com) --- Additional update: loading the RTL8821CE Wi-Fi-side driver dramatically improves Bluetooth HFP/mSBC RX stability on this RTL8821CE combo module. Hardware topology: - Bluetooth: Realtek `0bda:c821`, internal USB Full-Speed device, handled by `btusb` - Wi-Fi: Realtek RTL8821CE PCIe `10ec:c821`, handled by `rtw88_8821ce` / `rtw_8821ce` I ran the same near/far/near2 Bluetooth HFP microphone range test twice: 1. Wi-Fi driver not loaded. 2. Wi-Fi driver loaded manually, but Wi-Fi radio kept disabled in NetworkManager. State during the improved run: ```text 02:00.0 Network controller [0280]: Realtek Semiconductor Co., Ltd. RTL8821CE 802.11ac PCIe Wireless Network Adapter [10ec:c821] Kernel driver in use: rtw_8821ce Kernel modules: rtw88_8821ce WIFI-HW WIFI WWAN-HW WWAN enabled disabled missing enabled wlp2s0 DOWN ``` Kernel log also showed the Wi-Fi firmware initialized: ```text rtw_8821ce 0000:02:00.0: Firmware version 24.11.0, H2C version 12 ``` Results: | run | Wi-Fi driver | phase | RSSI avg | RSSI min | RX markers | RX bad se= q/k | RX bad dist/k | TX bad seq | TX bad dist | |---|---|---|---:|---:|---:|---:|---:|---:|---:| | `range-sco-test-20260531-005925` | not loaded | near | -38.9 | -42 | 1976= | 1.01 | 3.54 | 0 | 0 | | `range-sco-test-20260531-005925` | not loaded | far | -58.1 | -70 | 3528 | 123.30 | 103.74 | 0 | 0 | | `range-sco-test-20260531-005925` | not loaded | near2 | -49.6 | -54 | 193= 6 | 38.74 | 31.51 | 0 | 0 | | `range-sco-test-20260531-010648` | loaded, Wi-Fi radio off | near | -46.7= | -52 | 1975 | 1.01 | 1.01 | 0 | 0 | | `range-sco-test-20260531-010648` | loaded, Wi-Fi radio off | far | -53.9 | -60 | 3989 | 2.51 | 2.51 | 0 | 0 | | `range-sco-test-20260531-010648` | loaded, Wi-Fi radio off | near2 | -53.= 1 | -64 | 1984 | 6.55 | 6.55 | 0 | 0 | The important result is the far phase: - RX bad sequence rate dropped from `123.30/k` to `2.51/k`. - RX bad distance rate dropped from `103.74/k` to `2.51/k`. - TX remained clean in both runs. - RSSI no longer collapsed to `-70 dBm`; the improved run bottomed at `-60 dBm`. Because Wi-Fi remained disabled and the interface stayed down, this improve= ment does not appear to come from active Wi-Fi traffic. It appears to come from = the Wi-Fi-side driver/firmware initialization of the same RTL8821CE combo chip. This strongly suggests that the Linux Bluetooth-only initialization path for `0bda:c821` leaves the combo chip in a worse Bluetooth RX/range state than = the state after `rtw_8821ce` initializes the Wi-Fi side. The likely area is Rea= ltek combo-chip coexistence/RF/antenna-path/shared firmware state. Practical workaround on this machine: - keep `rtw88_8821ce` loadable and loaded at boot; - keep Wi-Fi radio disabled if Wi-Fi is not needed. Local captures/reports: - `captures/range-sco-test-20260531-005925.snoop` - `captures/range-sco-test-20260531-005925-metrics.csv` - `reports/range-sco-test-20260531-005925-analysis.md` - `captures/range-sco-test-20260531-010648.snoop` - `captures/range-sco-test-20260531-010648-metrics.csv` - `reports/range-sco-test-20260531-010648-analysis.md` - `reports/rtl8821ce-wifi-driver-coex-range-comparison-20260531.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.=