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 10:16:25 +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 07/04/2016 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?

Best regards,
Krzysztof