linux-kernel - Re: [PATCH v3 0/8] NVIDIA Tegra clocksource driver improvements

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Message-ID: <26aeb9f0-5eb1-005a-02c1-4d785fe70331@linaro.org>
Date:   Fri, 31 May 2019 22:31:11 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Joseph Lo <josephl@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nicolas Chauvet <kwizart@...il.com>
Subject: Re: [PATCH v3 0/8] NVIDIA Tegra clocksource driver improvements

On 31/05/2019 14:33, Dmitry Osipenko wrote:
> 31.05.2019 11:26, Peter De Schrijver пишет:
>> On Fri, May 24, 2019 at 06:32:45PM +0300, Dmitry Osipenko wrote:
>>> Hello,
>>>
>>> This series primarily unifies the driver code across all Tegra SoC
>>> generations. In a result the clocksources are allocated per-CPU on
>>> older Tegra's and have a higher rating than the arch-timer, the newer
>>> Tegra210 is getting support for microsecond clocksource and the driver's
>>> code is getting much cleaner. Note that arch-timer usage is discouraged on
>>> all Tegra's due to the time jitter caused by the CPU frequency scaling.
>>
>> I think the limitations are more as follows:
>>
>> Chip	timer		suffers cpu dvfs jitter		can wakeup from cc7
>> T20	us-timer	No				Yes
>> T20	twd timer	Yes				No?
>> T30	us-timer	No				Yes
>> T30	twd timer	Yes				No?
>> T114	us-timer	No				Yes
>> T114	arch timer	No				Yes
>> T124	us-timer	No				Yes
>> T124	arch timer	No				Yes
>> T210	us-timer	No				Yes
>> T210	arch timer	No				No
>> T210	clk_m timer	No				Yes
>>
>> right?
> 
> Doesn't arch timer run off the CPU clock? If yes (that's what I
> assumed), then it should be affected by the DVFS. Otherwise I'll lower
> the clocksource's rating for T114/124/132.
> 
> TWD can't wake CPU from the power-down state, so it's a solid "No" for
> TWD in the "can wakeup from cc7" column.

Wouldn't make sense to rename the timer-tegra20.c to timer-tegra.c now ?


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