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Sun, 11 Jan 2026 16:10:50 -0800 (PST) Received: from localhost.localdomain ([178.224.217.169]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6507be641e0sm16003130a12.22.2026.01.11.16.10.49 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sun, 11 Jan 2026 16:10:50 -0800 (PST) From: Marnix Rijnart To: Greg Kroah-Hartman , Jiri Slaby Cc: linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, regressions@lists.linux.dev, Marnix Rijnart , stable@vger.kernel.org Subject: [PATCH v3] serial: 8250_pci: Fix broken RS485 for F81504/508/512 Date: Mon, 12 Jan 2026 01:08:23 +0100 Message-ID: <20260112000931.61703-1-marnix.rijnart@iwell.eu> X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Fintek F81504/508/512 can support both RTS_ON_SEND and RTS_AFTER_SEND,=20 but pci_fintek_rs485_supported only announces the former. This makes it impossible to unset SER_RS485_RTS_ON_SEND from=20 userspace because of uart_sanitize_serial_rs485(). Some devices=20 with these chips need RTS low on TX, so they are effectively broken. Fix this by announcing the support for SER_RS485_RTS_AFTER_SEND, similar to commit 068d35a7be65 ("serial: sc16is7xx: announce support=20 for SER_RS485_RTS_ON_SEND"). Fixes: 4afeced55baa ("serial: core: fix sanitizing check for RTS settings") Cc: stable@vger.kernel.org Signed-off-by: Marnix Rijnart --- Changes in v3: - Rewrite commit message to clarify problem - Use longer commit hashes - v2: https://patch.msgid.link/20260111135933.31316-1-marnix.rijnart@iwell.= eu Changes in v2: - Added fixes tags - Cc stable - v1: https://patch.msgid.link/20250923221756.26770-1-marnix.rijnart@iwell= .eu --- drivers/tty/serial/8250/8250_pci.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8= 250_pci.c index 152f914c599d..a9da222bd174 100644 --- a/drivers/tty/serial/8250/8250_pci.c +++ b/drivers/tty/serial/8250/8250_pci.c @@ -1645,7 +1645,7 @@ static int pci_fintek_rs485_config(struct uart_port *= port, struct ktermios *term } =20 static const struct serial_rs485 pci_fintek_rs485_supported =3D { - .flags =3D SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND, + .flags =3D SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTE= R_SEND, /* F81504/508/512 does not support RTS delay before or after send */ }; =20 --=20 2.52.0