linux-serial-test: add patch to fix serial setup handling

Add patch that restores user intent in serial setup handling. Upstream
commit 77320571e63c ignores user input when RS485 was pre-configured,
breaking loopback and flow-control tests.

This patch ensures RS485 can be explicitly controlled while still
respecting pre-existing configurations when appropriate.

Signed-off-by: Vitor Soares <vitor.soares@toradex.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-oe/recipes-test/linux-serial-test/files/0001-Fix-serial-setup-handling-to-respect-user-intent.patch

@@ -0,0 +1,133 @@
+From 8d4f9a1a77f59eb3ed79267f58fac949835aebfc Mon Sep 17 00:00:00 2001
+From: Vitor Soares <vitor.soares@toradex.com>
+Date: Thu, 30 Oct 2025 14:52:57 +0000
+Subject: [PATCH] Fix serial setup handling to respect user intent
+
+Commit 77320571e63c ("Check if rs485 is already configured on the port")
+attempted to respect RS485 settings already configured on the port (e.g.
+via Device Tree). However, it unintentionally ignored user input,
+causing issues such as:
+- Inability to change delay settings
+- Failure to explicitly disable RS485
+- Broken UART loopback and RTS/CTS flow-control tests when RS485 was
+pre-enabled
+
+The original intent was valid for existing configurations (bare -q), but
+the tool should prioritize user intent, especially in testing scenarios.
+
+This update restores predictable, user-driven behavior:
+- RS485 can be explicitly enabled, disabled, or reconfigured
+- Current configurations are respected when appropriate
+
+Upstream-Status: Submitted [https://github.com/cbrake/linux-serial-test/pull/68]
+Fixes: 77320571e63c ("Check if rs485 is already configured on the port")
+Signed-off-by: Vitor Soares <vitor.soares@toradex.com>
+---
+ linux-serial-test.c | 48 ++++++++++++++++++++++++++++-----------------
+ 1 file changed, 30 insertions(+), 18 deletions(-)
+
+diff --git a/linux-serial-test.c b/linux-serial-test.c
+index 294f53882570..119bf58e663d 100644
+--- a/linux-serial-test.c
++++ b/linux-serial-test.c
+@@ -60,6 +60,7 @@ int _cl_no_tx_param = 0;
+ int _cl_rx_delay = 0;
+ int _cl_tx_delay = 0;
+ int _cl_tx_bytes = 0;
++int _cl_rs485 = 0;
+ int _cl_rs485_after_delay = -1;
+ int _cl_rs485_before_delay = 0;
+ int _cl_rs485_rts_after_send = 0;
+@@ -315,7 +316,9 @@ static void display_help(void)
+ 			"  -q, --rs485              Enable RS485 direction control on port, and set delay from when TX is\n"
+ 			"                           finished and RS485 driver enable is de-asserted. Delay is specified in\n"
+ 			"                           bit times. To optionally specify a delay from when the driver is enabled\n"
+-			"                           to start of TX use 'after_delay.before_delay' (-q 1.1)\n"
++			"                           to start of TX use 'after_delay.before_delay' (-q 1.1). If no value is\n"
++			"                           given, delay defaults to 0. Existing RS485 configuration is respected if\n"
++			"                           already enabled.\n"
+ 			"  -Q, --rs485_rts          Deassert RTS on send, assert after send. Omitting -Q inverts this logic.\n"
+ 			"  -m, --no-modem           Do not clobber against any modem lines.\n"
+ 			"  -o, --tx-time            Number of seconds to transmit for (defaults to 0, meaning no limit)\n"
+@@ -335,7 +338,7 @@ static void process_options(int argc, char * argv[])
+ {
+ 	for (;;) {
+ 		int option_index = 0;
+-		static const char *short_options = "hb:p:d:D:TRsSy:z:cBertq:Qml:a:w:o:i:P:kKAI:O:W:Znf";
++		static const char *short_options = "hb:p:d:D:TRsSy:z:cBertq::Qml:a:w:o:i:P:kKAI:O:W:Znf";
+ 		static const struct option long_options[] = {
+ 			{"help", no_argument, 0, 0},
+ 			{"baud", required_argument, 0, 'b'},
+@@ -359,7 +362,7 @@ static void process_options(int argc, char * argv[])
+ 			{"rx-delay", required_argument, 0, 'l'},
+ 			{"tx-delay", required_argument, 0, 'a'},
+ 			{"tx-bytes", required_argument, 0, 'w'},
+-			{"rs485", required_argument, 0, 'q'},
++			{"rs485", optional_argument, 0, 'q'},
+ 			{"rs485_rts", no_argument, 0, 'Q'},
+ 			{"no-modem", no_argument, 0, 'm'},
+ 			{"tx-time", required_argument, 0, 'o'},
+@@ -467,8 +470,12 @@ static void process_options(int argc, char * argv[])
+ 		}
+ 		case 'q': {
+ 			char *endptr;
+-			_cl_rs485_after_delay = strtol(optarg, &endptr, 0);
+-			_cl_rs485_before_delay = strtol(endptr+1, &endptr, 0);
++			_cl_rs485 = 1;
++
++			if (optarg) {
++				_cl_rs485_after_delay = strtol(optarg, &endptr, 0);
++				_cl_rs485_before_delay = strtol(endptr+1, &endptr, 0);
++			}
+ 			break;
+ 		}
+ 		case 'Q':
+@@ -707,15 +714,20 @@ static void setup_serial_port(int baud)
+ 
+ 	/* enable/disable rs485 direction control, first check if RS485 is supported */
+ 	if(ioctl(_fd, TIOCGRS485, &rs485) < 0) {
+-		if (_cl_rs485_after_delay >= 0) {
++		if (_cl_rs485) {
+ 			/* error could be because hardware is missing rs485 support so only print when actually trying to activate it */
+ 			perror("Error getting RS-485 mode");
+ 		}
+ 	} else {
+-		if (rs485.flags & SER_RS485_ENABLED) {
+-			printf("RS485 already enabled on port, ignoring delays if set\n");
+-		} else {
+-			if (_cl_rs485_after_delay >= 0) {
++		if (_cl_rs485) {
++			/* Skip reconfiguration if already enabled with default delays */
++			if ((_cl_rs485_after_delay < 0) && (rs485.flags & SER_RS485_ENABLED)) {
++				printf("RS485 already enabled on port with default settings\n");
++			} else {
++				/* Default to 0 if not specified */
++				if (_cl_rs485_after_delay < 0) {
++					_cl_rs485_after_delay = 0;
++				}
+ 				/* enable RS485 */
+ 				rs485.flags |= SER_RS485_ENABLED | SER_RS485_RX_DURING_TX |
+ 					(_cl_rs485_rts_after_send ? SER_RS485_RTS_AFTER_SEND : SER_RS485_RTS_ON_SEND);
+@@ -725,14 +737,14 @@ static void setup_serial_port(int baud)
+ 				if(ioctl(_fd, TIOCSRS485, &rs485) < 0) {
+ 					perror("Error setting RS-485 mode");
+ 				}
+-			} else {
+-				/* disable RS485 */
+-				rs485.flags &= ~(SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND);
+-				rs485.delay_rts_after_send = 0;
+-				rs485.delay_rts_before_send = 0;
+-				if(ioctl(_fd, TIOCSRS485, &rs485) < 0) {
+-					perror("Error setting RS-232 mode");
+-				}
++			}
++		} else {
++			/* disable RS485 */
++			rs485.flags &= ~(SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND);
++			rs485.delay_rts_after_send = 0;
++			rs485.delay_rts_before_send = 0;
++			if(ioctl(_fd, TIOCSRS485, &rs485) < 0) {
++				perror("Error setting RS-232 mode");
+ 			}
+ 		}
+ 	}

meta-oe/recipes-test/linux-serial-test/linux-serial-test_git.bb

@@ -6,6 +6,7 @@ LIC_FILES_CHKSUM = "file://LICENSES/MIT;md5=544799d0b492f119fa04641d1b8868ed"
 SRC_URI = "git://github.com/cbrake/linux-serial-test.git;protocol=https;branch=master \
            file://0001-linux-serial-test.c-fix-returned-error-code.patch \
            file://0002-linux-serial-test.c-fix-potential-hang-in-while-loop.patch \
+           file://0001-Fix-serial-setup-handling-to-respect-user-intent.patch \
 "
 PV = "0+git"
 SRCREV = "1a81f3c7be086ee01a9be8589a606426276c86d5"