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

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

[Heiko Stübner]

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@sntech.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

Re: [PATCH] serial: samsung: move clock deactivation below uart registration

[Tomasz Figa]

Hi Heiko,

On Thursday 05 of December 2013 00:54:38 Heiko Stübner wrote:
> 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@sntech.de>
> ---
>  drivers/tty/serial/samsung.c |    8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)

Makes sense.

Reviewed-by: Tomasz Figa <t.figa@samsung.com>

Best regards,
Tomasz

Re: [PATCH] serial: samsung: move clock deactivation below uart registration

[Heiko Stübner]

Hi Greg,

just wanted to ask about the state of this patch. I can see it in your branch 
named "fixes" [0] but it seems it hasn't made its way into the kernel neither 
during the 3.13-rcs or with your 3.14-pull [1].


Thanks
Heiko


[0] https://git.kernel.org/cgit/linux/kernel/git/gregkh/tty.git/log/?h=fixes
[1] 
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=bcee63488ece9a0fca8be19951428a7b41001e66


Am Donnerstag, 5. Dezember 2013, 00:54:38 schrieb Heiko Stübner:
> 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@sntech.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)

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Re: [PATCH] serial: samsung: move clock deactivation below uart registration

[Greg Kroah-Hartman]

On Tue, Jan 21, 2014 at 03:26:42PM +0100, Heiko Stübner wrote:
> Hi Greg,
> 
> just wanted to ask about the state of this patch. I can see it in your branch 
> named "fixes" [0] but it seems it hasn't made its way into the kernel neither 
> during the 3.13-rcs or with your 3.14-pull [1].
> 
> 
> Thanks
> Heiko
> 
> 
> [0] https://git.kernel.org/cgit/linux/kernel/git/gregkh/tty.git/log/?h=fixes
> [1] 
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=bcee63488ece9a0fca8be19951428a7b41001e66

Ah crap, I missed this, sorry, I'll get it to Linus in time for
3.14-final, sorry about that.

greg k-h
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