linux-kernel - Re: [RFC PATCH 2/2] rtc: s3c: Add s3c_rtc_{enable/disable}_clk in s3c_rtc

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Message-id: <577B762F.6020609@samsung.com>
Date:	Tue, 05 Jul 2016 10:56:15 +0200
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Alim Akhtar <alim.akhtar@...sung.com>, rtc-linux@...glegroups.com,
	linux-kernel@...r.kernel.org
Cc:	alexandre.belloni@...e-electrons.com, javier@....samsung.com,
	pankaj.dubey@...sung.com
Subject: Re: [RFC PATCH 2/2] rtc: s3c: Add s3c_rtc_{enable/disable}_clk in
 s3c_rtc_setfreq()

On 07/05/2016 10:52 AM, Alim Akhtar wrote:
> 
> 
> On 07/05/2016 01:46 PM, Krzysztof Kozlowski wrote:
>> On 07/04/2016 01:03 PM, Alim Akhtar wrote:
>>> As per code flow it is possible that s3c_rtc_setfreq() might get called
>>> with rtc clock disabled and in set_freq we perform h/w registers
>>> read/write,
>>> which might results in a kernel crash while probing rtc driver.
>>> Below is one such case:
>>> s3c_rtc_probe()
>>>      clk_prepare_enable(info->rtc_clk) // rtc clock enabled
>>>        s3c_rtc_gettime() // will enable clk if not done, and disable
>>> it upon exit
>>>          s3c_rtc_setfreq() //then this will be called with clk disabled
>>
>> The indentation suggests levels of calls (chain) not sequence. This
>> should be:
>> s3c_rtc_probe()
>>    clk_prepare_enable(info->rtc_clk) // rtc clock enabled
>>    s3c_rtc_gettime() // will enable clk if not done, and disable it
>> upon exit
>>    s3c_rtc_setfreq() //then this will be called with clk disabled
>>
>>>
>>> This patch take cares of such issue by adding
>>> s3c_rtc_{enable/disable}_clk in
>>> s3c_rtc_setfreq().
>>
>> What I don't get is that you wrote "it is *possible* that
>> s3c_rtc_setfreq() *might* get called". From my understanding this will
>> happen always because src_rtc_gettime() always disables the clocks.
>>
>> Why it does not happen always?
>>
> 
> Yes, you are right, it is always disabled when reaches s3c_rtc_setfreq().
> And I observed a kernel crash while testing on exynos7 platform in
> s3c_rtc_setfreq() because clock was always disabled at this point. And
> this patches fixes this issue.

Ok, thanks! Could you adjust the commit message mentioning that it
always causes crash on Exynos 7 platform and adding:

Fixes: 24e1455493da ("drivers/rtc/rtc-s3c.c: delete duplicate clock
control")
Cc: <stable@...r.kernel.org>

Reviewed-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>

Best regards,
Krzysztof