Re: [RFC PATCH 2/2] rtc: s3c: Add s3c_rtc_{enable/disable}_clk in s3c_rtc_setfreq()

pankaj.dubey
2016-07-05T09:41:30Z

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@vger.kernel.org>
>
> Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
>

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

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

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

Thanks,
Pankaj Dubey

> Best regards,
> Krzysztof
>
>