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

[Alim Akhtar]

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.


> Best regards,
> Krzysztof