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

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Date:	Tue, 05 Jul 2016 15:13:13 +0530
From:	"pankaj.dubey" <pankaj.dubey@...sung.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	rtc-linux@...glegroups.com, linux-kernel@...r.kernel.org
Cc:	alexandre.belloni@...e-electrons.com, javier@....samsung.com
Subject: Re: [RFC PATCH 2/2] rtc: s3c: Add s3c_rtc_{enable/disable}_clk in
 s3c_rtc_setfreq()

Hi Alim,

On Tuesday 05 July 2016 02:26 PM, Krzysztof Kozlowski wrote:
> 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>
> 

After addressing Krzysztof's review comments, Please feel free to add

Reviewed-by: Pankaj Dubey <pankaj.dubey@...sung.com>

For testing on Exynos7420
Tested-by: Pankaj Dubey <pankaj.dubey@...sung.com>

Thanks,
Pankaj Dubey

> Best regards,
> Krzysztof
> 
>