linux-kernel - [PATCH 4.9 37/47] tty: serial: imx: keep console clocks always on

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Date:   Mon, 23 Nov 2020 13:22:23 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Fugang Duan <fugang.duan@....com>
Subject: [PATCH 4.9 37/47] tty: serial: imx: keep console clocks always on

From: Fugang Duan <fugang.duan@....com>

commit e67c139c488e84e7eae6c333231e791f0e89b3fb upstream.

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.

Fixes: 1cf93e0d5488 ("serial: imx: remove the uart_console() check")
Acked-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Signed-off-by: Fugang Duan <fugang.duan@....com>
Link: https://lore.kernel.org/r/20201111025136.29818-1-fugang.duan@nxp.com
Cc: stable <stable@...r.kernel.org>
[fix up build warning - gregkh]
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1787,16 +1787,6 @@ imx_console_write(struct console *co, co
 	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;
@@ -1832,9 +1822,6 @@ imx_console_write(struct console *co, co
 
 	if (locked)
 		spin_unlock_irqrestore(&sport->port.lock, flags);
-
-	clk_disable(sport->clk_ipg);
-	clk_disable(sport->clk_per);
 }
 
 /*
@@ -1935,15 +1922,14 @@ imx_console_setup(struct console *co, ch
 
 	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;