linux-kernel - [REGRESSION][PATCH] serial: 8250_pci: Fix broken RS485 for F81504/508/512

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <20250923221756.26770-1-marnix.rijnart@iwell.eu>
Date: Wed, 24 Sep 2025 00:17:33 +0200
From: Marnix Rijnart <marnix.rijnart@...ll.eu>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>
Cc: Marnix Rijnart <marnix.rijnart@...ll.eu>,
	linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	regressions@...ts.linux.dev
Subject: [REGRESSION][PATCH] serial: 8250_pci: Fix broken RS485 for F81504/508/512

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.

Signed-off-by: Marnix Rijnart <marnix.rijnart@...ll.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/8250/8250_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
 }
 
 static const struct serial_rs485 pci_fintek_rs485_supported = {
-	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND,
+	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND,
 	/* F81504/508/512 does not support RTS delay before or after send */
 };
 
-- 
2.51.0