FAILED: patch "[PATCH] serial: 8250_dw: Do not reclock if already at correct rate" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x e5d6bd25f93d6ae158bb4cd04956cb497a85b8ef
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024032710-unbent-dingy-2b33@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

e5d6bd25f93d ("serial: 8250_dw: Do not reclock if already at correct rate") 74365bc138ab ("serial: 8250_dw: drop bogus uartclk optimisation") 0eb9da9cf201 ("serial: 8250_dw: Fix the trivial typo in the comment")

thanks,

greg k-h

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

From e5d6bd25f93d6ae158bb4cd04956cb497a85b8ef Mon Sep 17 00:00:00 2001
From: Peter Collingbourne <[email protected]>
Date: Thu, 22 Feb 2024 11:26:34 -0800
Subject: [PATCH] serial: 8250_dw: Do not reclock if already at correct rate

When userspace opens the console, we call set_termios() passing a termios with the console's configured baud rate. Currently this causes dw8250_set_termios() to disable and then re-enable the UART clock at the same frequency as it was originally. This can cause corruption of any concurrent console output. Fix it by skipping the reclocking if we are already at the correct rate.

index 2d1f350a4bea..c1d43f040c43 100644
@@ -357,9 +357,9 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios,
 	long rate;
 	int ret;
 
-	clk_disable_unprepare(d->clk);
 	rate = clk_round_rate(d->clk, newrate);
-	if (rate > 0) {
+	if (rate > 0 && p->uartclk != rate) {
+		clk_disable_unprepare(d->clk);
 		/*
 		 * Note that any clock-notifer worker will block in
 		 * serial8250_update_uartclk() until we are done.

@@ -367,8 +367,8 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios,
 		ret = clk_set_rate(d->clk, newrate);
 		if (!ret)
 			p->uartclk = rate;
+		clk_prepare_enable(d->clk);
 	}
-	clk_prepare_enable(d->clk);
 
 	dw8250_do_set_termios(p, termios, old);
 }