patch "tty: serial: imx: keep console clocks always on" added to tty-linus

This is a note to let you know that I've just added the patch titled

tty: serial: imx: keep console clocks always on

to my tty git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From e67c139c488e84e7eae6c333231e791f0e89b3fb Mon Sep 17 00:00:00 2001
From: Fugang Duan <[email protected]>
Date: Wed, 11 Nov 2020 10:51:36 +0800
Subject: tty: serial: imx: keep console clocks always on
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

For below code, there has chance to cause deadlock in SMP system:
Thread 1:
clk_enable_lock();
pr_info("debug message");
clk_enable_unlock();

Thread 2:
imx_uart_console_write()

	clk_enable()
		clk_enable_lock();

Thread 1:
Acuired clk enable_lock -> printk -> console_trylock_spinning
Thread 2:
console_unlock() -> imx_uart_console_write -> clk_disable -> Acquite clk enable_lock

So the patch is to keep console port clocks always on like other console drivers.

---
 drivers/tty/serial/imx.c | 20 +++-----------------
 1 file changed, 3 insertions(+), 17 deletions(-)

index 3c53a3c89959..cacf7266a262 100644
@@ -2008,16 +2008,6 @@ imx_uart_console_write(struct console *co, const char *s, unsigned int count)
 	unsigned int ucr1;
 	unsigned long flags = 0;
 	int locked = 1;
-	int retval;
-
-	retval = clk_enable(sport->clk_per);
-	if (retval)
-		return;
-	retval = clk_enable(sport->clk_ipg);
-	if (retval) {
-		clk_disable(sport->clk_per);
-		return;
-	}
 
 	if (sport->port.sysrq)
 		locked = 0;

@@ -2053,9 +2043,6 @@ imx_uart_console_write(struct console *co, const char *s, unsigned int count)
 
 	if (locked)
 		spin_unlock_irqrestore(&sport->port.lock, flags);
-
-	clk_disable(sport->clk_ipg);
-	clk_disable(sport->clk_per);
 }
 
 /*

@@ -2156,15 +2143,14 @@ imx_uart_console_setup(struct console *co, char *options)
 
 	retval = uart_set_options(&sport->port, co, baud, parity, bits, flow);
 
-	clk_disable(sport->clk_ipg);
 	if (retval) {
-		clk_unprepare(sport->clk_ipg);
+		clk_disable_unprepare(sport->clk_ipg);
 		goto error_console;
 	}
 
-	retval = clk_prepare(sport->clk_per);
+	retval = clk_prepare_enable(sport->clk_per);
 	if (retval)
-		clk_unprepare(sport->clk_ipg);
+		clk_disable_unprepare(sport->clk_ipg);
 
 error_console:
 	return retval;

2.29.2