linux-kernel - [PATCH] serial: samsung: move clock deactivation below uart registration

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Message-Id: <201312050054.39327.heiko@sntech.de>
Date:	Thu, 5 Dec 2013 00:54:38 +0100
From:	Heiko Stübner <heiko@...ech.de>
To:	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Cc:	Jiri Slaby <jslaby@...e.cz>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
	Kukjin Kim <kgene.kim@...sung.com>,
	Chander Kashyap <chander.kashyap@...aro.org>
Subject: [PATCH] serial: samsung: move clock deactivation below uart registration

Commit 60e93575476f (serial: samsung: enable clock before clearing pending
interrupts during init) added handling of the controller clock during init.

On most systems this clock is also one of the baud_clock sources and
possibly used by the earlycon and thus already enabled by the bootloader.

Therefore a gap exists between s3c24xx_serial_init_port disabling the
clock and an attached console reenabling it, making the transition from
earlycon to regular console possibly hang the system - as seen on my
S3C2442 based Freerunner today.

Therefore move the disabling of the clock from s3c24xx_serial_init_port
below the uart port registration, effectively creating an overlap and
keeping the clock running non-stop if the console wants to grab this port.

Signed-off-by: Heiko Stuebner <heiko@...ech.de>
---
 drivers/tty/serial/samsung.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/samsung.c b/drivers/tty/serial/samsung.c
index c1af04d..9cd706d 100644
--- a/drivers/tty/serial/samsung.c
+++ b/drivers/tty/serial/samsung.c
@@ -1209,7 +1209,6 @@ static int s3c24xx_serial_init_port(struct s3c24xx_uart_port *ourport,
 
 	/* reset the fifos (and setup the uart) */
 	s3c24xx_serial_resetport(port, cfg);
-	clk_disable_unprepare(ourport->clk);
 	return 0;
 }
 
@@ -1287,6 +1286,13 @@ static int s3c24xx_serial_probe(struct platform_device *pdev)
 	uart_add_one_port(&s3c24xx_uart_drv, &ourport->port);
 	platform_set_drvdata(pdev, &ourport->port);
 
+	/*
+	 * Deactivate the clock enabled in s3c24xx_serial_init_port here,
+	 * so that a potential re-enablement through the pm-callback overlaps
+	 * and keeps the clock enabled in this case.
+	 */
+	clk_disable_unprepare(ourport->clk);
+
 #ifdef CONFIG_SAMSUNG_CLOCK
 	ret = device_create_file(&pdev->dev, &dev_attr_clock_source);
 	if (ret < 0)
-- 
1.7.10.4

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