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

[Dmitry Osipenko]

31.05.2019 11:26, Peter De Schrijver ÐÐÑÐÑ:
> 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.