Re: [PATCH] serial: samsung: Reorder the sequence of clock control when call s3c24xx_serial_set_termios()

[Marek Szyprowski]

Dear Chanwoo,

On 2016-03-25 01:10, Chanwoo Choi wrote:
> Hi Robert,
>
> I send following patch to fix the broken serial log of Exynos SoC.
> As I knew, you also knew this issue.
> If possible, could you review or test this patch?

Robert no longer works for Samsung, so I'm afraid that he won't be able 
to test
this patch.

> Best Regards,
> Chanwoo Choi
>
> On 2016ë 03ì 14ì 09:41, 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@xxxxxxxxxxx>
> > ---
> >   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 d72cd736bdc6..80d59dbfebba 100644
> > --- a/drivers/tty/serial/samsung.c
> > +++ b/drivers/tty/serial/samsung.c
> > @@ -1265,13 +1265,13 @@ static void s3c24xx_serial_set_termios(struct uart_port *port,
> >   	if (ourport->baudclk != clk) {
> >   		s3c24xx_serial_setsource(port, clk_sel);
> >   
> > +		clk_prepare_enable(clk);
> > +

IMHO clk_prepare_enable() should be moved before 
s3c24xx_serial_setsource() to be
really sure that there will be no period of hw operating with disabled 
baud clock.
Could you check if it works for you?

> >   		if (!IS_ERR(ourport->baudclk)) {
> >   			clk_disable_unprepare(ourport->baudclk);
> >   			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