[rtc-linux] 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:

quoted

On 07/04/2016 01:03 PM, Alim Akhtar wrote:

quoted

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

quoted

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: <redacted>

Reviewed-by: Krzysztof Kozlowski <redacted>

Best regards,
Krzysztof

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