Re: [PATCH v3 0/8] NVIDIA Tegra clocksource driver improvements
From: Peter De Schrijver
Date: Mon Jun 03 2019 - 03:21:41 EST
On Fri, May 31, 2019 at 03:33:41PM +0300, Dmitry Osipenko wrote:
> 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.
No. It doesn't. This is the big change between A9 and later CPUs.
> 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.