linux-kernel - Re: [PATCH v5] clk: samsung: Prevent potential endless loop in the PLL ops

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Message-ID: <cbc83ec7-57f3-8ced-34c6-8df5e0541fe9@kernel.org>
Date:   Mon, 23 Nov 2020 11:20:09 +0100
From:   Sylwester Nawrocki <snawrocki@...nel.org>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Sylwester Nawrocki <s.nawrocki@...sung.com>,
        linux-clk@...r.kernel.org, tomasz.figa@...il.com,
        cw00.choi@...sung.com, m.szyprowski@...sung.com, sboyd@...nel.org,
        mturquette@...libre.com, b.zolnierkie@...sung.com,
        linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH v5] clk: samsung: Prevent potential endless loop in the
 PLL ops

On 11/22/20 16:16, Krzysztof Kozlowski wrote:
> On Fri, Nov 20, 2020 at 04:57:31PM +0100, Sylwester Nawrocki wrote:
>> The PLL status polling loops in the set_rate callbacks of some PLLs
>> have no timeout detection and may become endless loops when something
>> goes wrong with the PLL.
>>
>> For some PLLs there is already the ktime API based timeout detection,
>> but it will not work in all conditions when .set_rate gets called.
>> In particular, before the clocksource is initialized or when the
>> timekeeping is suspended.
>>
>> This patch adds a common helper with the PLL status bit polling and
>> timeout detection. For conditions where the timekeeping API should not
>> be used a simple readl_relaxed/cpu_relax() busy loop is added with the
>> iterations limit derived from measurements of readl_relaxed() execution
>> time for various PLL types and Exynos SoCs variants.
>>
>> Actual PLL lock time depends on the P divider value, the VCO frequency
>> and a constant PLL type specific LOCK_FACTOR and can be calculated as
>>
>>   lock_time = Pdiv * LOCK_FACTOR / VCO_freq
>>
>> For the ktime API use cases a common timeout value of 20 ms is applied
>> for all the PLLs with an assumption that maximum possible value of Pdiv
>> is 64, maximum possible LOCK_FACTOR value is 3000 and minimum VCO
>> frequency is 24 MHz.
>>
>> Signed-off-by: Sylwester Nawrocki<s.nawrocki@...sung.com>

> Reviewed-by: Krzysztof Kozlowski<krzk@...nel.org>

Thanks, patch applied.

--
Regards,
Sylwester