linux-kernel - Re: [PATCH] serial: samsung: Reorder the sequence of clock control when call s3c24xx_serial_set

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Date:	Fri, 25 Mar 2016 17:22:31 +0900
From:	Chanwoo Choi <cw00.choi@...sung.com>
To:	Marek Szyprowski <m.szyprowski@...sung.com>,
	gregkh@...uxfoundation.org, jslaby@...e.com
Cc:	k.kozlowski@...sung.com, kgene@...nel.org,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org,
	"Robert Baldyga (SRPOL)" <r.baldyga@...sung.com>
Subject: Re: [PATCH] serial: samsung: Reorder the sequence of clock control
 when call s3c24xx_serial_set_termios()

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@...sung.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