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

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

[Chanwoo Choi]

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>
---
 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);
+
 		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;
 	}
-- 
1.9.1

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

[Chanwoo Choi]

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?

Best Regards,
Chanwoo Choi

On 2016년 03월 14일 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@samsung.com>
> ---
>  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);
> +
>  		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;
>  	}
> 

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 2016년 03월 14일 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@samsung.com>
>> ---
>>   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

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

[Chanwoo Choi]

Dear Marek,

On 2016년 03월 25일 17:14, Marek Szyprowski wrote:
> 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.

Ah. Thanks for your reply.

> 
>> Best Regards,
>> Chanwoo Choi
>>
>> On 2016년 03월 14일 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@samsung.com>
>>> ---
>>>   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?

Yes. I tested it without any problem.
But, as you commented, clk_prepare_enable() should be called before s3c24xx_serial_setsource().

I'll modify it.

> 
>>>           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

Best Regards,
Chanwoo Choi