Subject: Re: [PATCH v2] serial: samsung: Reorder the sequence of clock control
 when call s3c24xx_serial_set_termios()
To: Chanwoo Choi <cw00.choi@samsung.com>, gregkh@linuxfoundation.org,
        jslaby@suse.com
References: <1459122503-5202-1-git-send-email-cw00.choi@samsung.com>
Cc: k.kozlowski@samsung.com, kgene@kernel.org, linux-serial@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org
From: Marek Szyprowski <m.szyprowski@samsung.com>
Message-id: <56FA33A0.4040608@samsung.com>
Date: Tue, 29 Mar 2016 09:49:52 +0200
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Hello,

On 2016-03-28 01:48, Chanwoo Choi wrote:
> This patch fixes the broken serial log when changing the clock source
> of uart device. Before disabling the original clock source, this patch
> enables the new clock source to protect the clock off state for a split second.
>
> Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

Reviewed-by: Marek Szyprowski <m.szyprowski@samsung.com>

> ---
> Changes from v1:
> (https://lkml.org/lkml/2016/3/13/183)
> - Enable the clock before changing the source by s3c24xx_serial_setsource()
> - Rebase it on Linux v4.6-rc1
>
>   drivers/tty/serial/samsung.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/samsung.c b/drivers/tty/serial/samsung.c
> index ac7f8df54406..99bb23161dd6 100644
> --- a/drivers/tty/serial/samsung.c
> +++ b/drivers/tty/serial/samsung.c
> @@ -1271,6 +1271,8 @@ static void s3c24xx_serial_set_termios(struct uart_port *port,
>   	/* check to see if we need  to change clock source */
>   
>   	if (ourport->baudclk != clk) {
> +		clk_prepare_enable(clk);
> +
>   		s3c24xx_serial_setsource(port, clk_sel);
>   
>   		if (!IS_ERR(ourport->baudclk)) {
> @@ -1278,8 +1280,6 @@ static void s3c24xx_serial_set_termios(struct uart_port *port,
>   			ourport->baudclk = ERR_PTR(-EINVAL);
>   		}
>   
> -		clk_prepare_enable(clk);
> -
>   		ourport->baudclk = clk;
>   		ourport->baudclk_rate = clk ? clk_get_rate(clk) : 0;
>   	}

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland