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Sun, 11 Jan 2026 06:00:03 -0800 (PST) Received: from localhost.localdomain ([178.224.217.169]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6507b8c4048sm15488184a12.2.2026.01.11.06.00.03 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sun, 11 Jan 2026 06:00:03 -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 v2] serial: 8250_pci: Fix broken RS485 for F81504/508/512 Date: Sun, 11 Jan 2026 14:59:17 +0100 Message-ID: <20260111135933.31316-1-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" v1: https://patch.msgid.link/20250923221756.26770-1-marnix.rijnart@iwell.eu Changes:=20 * Added fixes tags * Cc stable Commit 4afeced ("serial: core: fix sanitizing check for RTS settings") introduced a regression making it impossible to unset SER_RS485_RTS_ON_SEND from userspace if SER_RS485_RTS_AFTER_SEND is unsupported. Because these devices need RTS to be low on TX (fecf27a) they are effectively broken. The hardware supports both RTS_ON_SEND and RTS_AFTER_SEND, so fix this by announcing support for SER_RS485_RTS_AFTER_SEND, similar to commit 068d35a. Fixes: 4afeced55baa ("serial: core: fix sanitizing check for RTS settings") Fixes: fecf27a373f5 ("serial: 8250_pci: add RS485 for F81504/508/512") Cc: stable@vger.kernel.org Signed-off-by: Marnix Rijnart --- 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