FAILED: patch "[PATCH] tty: serial: meson: fix hard LOCKUP on crtscts mode" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y
git checkout FETCH_HEAD
git cherry-pick -x 2a1d728f20edeee7f26dc307ed9df4e0d23947ab
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023112236-requisite-chomp-8664@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

2a1d728f20ed ("tty: serial: meson: fix hard LOCKUP on crtscts mode") 5b6806198347 ("serial: meson: Use platform_get_irq() to get the interrupt") 27d44e05d7b8 ("tty: serial: meson: retrieve port FIFO size from DT") 021212f53352 ("serial: meson: remove redundant initialization of variable id") dca3ac8d3bc9 ("tty/serial: Migrate meson_uart to use has_sysrq") a26988e8fef4 ("tty: serial: meson: if no alias specified use an available id")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2a1d728f20edeee7f26dc307ed9df4e0d23947ab Mon Sep 17 00:00:00 2001
From: Pavel Krasavin <[email protected]>
Date: Sat, 14 Oct 2023 11:39:26 +0000
Subject: [PATCH] tty: serial: meson: fix hard LOCKUP on crtscts mode

There might be hard lockup if we set crtscts mode on port without RTS/CTS configured:

# stty -F /dev/ttyAML6 crtscts; echo 1 > /dev/ttyAML6; echo 2 > /dev/ttyAML6
[   95.890386] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[   95.890857] rcu:     3-...0: (201 ticks this GP) idle=e33c/1/0x4000000000000000 softirq=5844/5846 fqs=4984
[   95.900212] rcu:     (detected by 2, t=21016 jiffies, g=7753, q=296 ncpus=4)
[   95.906972] Task dump for CPU 3:
[   95.910178] task:bash            state:R  running task     stack:0     pid:205   ppid:1      flags:0x00000202
[   95.920059] Call trace:
[   95.922485]  __switch_to+0xe4/0x168
[   95.925951]  0xffffff8003477508
[   95.974379] watchdog: Watchdog detected hard LOCKUP on cpu 3
[   95.974424] Modules linked in: 88x2cs(O) rtc_meson_vrtc

Possible solution would be to not allow to setup crtscts on such port.

Tested on S905X3 based board.

v6: stable tag added
v5: https://lore.kernel.org/lkml/[email protected]/
added missed Reviewed-by tags, Fixes tag added according to Dmitry and Neil notes
v4: https://lore.kernel.org/lkml/[email protected]/
More correct patch subject according to Jiri's note
v3: https://lore.kernel.org/lkml/[email protected]/
"From:" line added to the mail
v2: https://lore.kernel.org/lkml/[email protected]/
braces for single statement removed according to Dmitry's note
v1: https://lore.kernel.org/lkml/[email protected]/

index de298bf75d9b..8dd84617e715 100644
@@ -380,10 +380,14 @@ static void meson_uart_set_termios(struct uart_port *port,
 	else
 		val |= AML_UART_STOP_BIT_1SB;
 
-	if (cflags & CRTSCTS)
-		val &= ~AML_UART_TWO_WIRE_EN;
-	else
+	if (cflags & CRTSCTS) {
+		if (port->flags & UPF_HARD_FLOW)
+			val &= ~AML_UART_TWO_WIRE_EN;
+		else
+			termios->c_cflag &= ~CRTSCTS;
+	} else {
 		val |= AML_UART_TWO_WIRE_EN;
+	}
 
 	writel(val, port->membase + AML_UART_CONTROL);
 

@@ -705,6 +709,7 @@ static int meson_uart_probe(struct platform_device *pdev)
 	u32 fifosize = 64; /* Default is 64, 128 for EE UART_0 */
 	int ret = 0;
 	int irq;
+	bool has_rtscts;
 
 	if (pdev->dev.of_node)
 		pdev->id = of_alias_get_id(pdev->dev.of_node, "serial");

@@ -732,6 +737,7 @@ static int meson_uart_probe(struct platform_device *pdev)
 		return irq;
 
 	of_property_read_u32(pdev->dev.of_node, "fifo-size", &fifosize);
+	has_rtscts = of_property_read_bool(pdev->dev.of_node, "uart-has-rtscts");
 
 	if (meson_ports[pdev->id]) {
 		return dev_err_probe(&pdev->dev, -EBUSY,

@@ -762,6 +768,8 @@ static int meson_uart_probe(struct platform_device *pdev)
 	port->mapsize = resource_size(res_mem);
 	port->irq = irq;
 	port->flags = UPF_BOOT_AUTOCONF | UPF_LOW_LATENCY;
+	if (has_rtscts)
+		port->flags |= UPF_HARD_FLOW;
 	port->has_sysrq = IS_ENABLED(CONFIG_SERIAL_MESON_CONSOLE);
 	port->dev = &pdev->dev;
 	port->line = pdev->id;