17.06.2019 12:21, Thierry Reding пишет: > On Mon, Jun 17, 2019 at 02:47:43AM +0300, Dmitry Osipenko wrote: >> The minimum number of "cycles" is limited to 1 by >> clockevents_config_and_register(). > > Looks to me like cycles also depends on the multiplier and shift that > are computed for the clock source. It looks like the multiplier will > never be zero and the shift will always be such that it won't result in > a zero cycles either. But might be worth mentioning this in the commit > message. And it might be nice to also repeate that in a comment close to > the code, just to document this. > > It took me a couple of minutes to track this all down, so I think we > should take the same amount of time to document it so that we don't have > to go through it again once we've forgotten why we made this change. It's explicitly stated in the comment [1] what's the intent of the min_delta. But it's also good that you verified the clocksource code itself :) [1] https://elixir.bootlin.com/linux/v5.2-rc5/source/kernel/time/clockevents.c#L500 >> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx> >> --- >> drivers/clocksource/timer-tegra.c | 4 +--- >> 1 file changed, 1 insertion(+), 3 deletions(-) >> >> diff --git a/drivers/clocksource/timer-tegra.c b/drivers/clocksource/timer-tegra.c >> index f6a8eb0d7322..090c85358fe8 100644 >> --- a/drivers/clocksource/timer-tegra.c >> +++ b/drivers/clocksource/timer-tegra.c >> @@ -54,9 +54,7 @@ static int tegra_timer_set_next_event(unsigned long cycles, >> { >> void __iomem *reg_base = timer_of_base(to_timer_of(evt)); >> >> - writel_relaxed(TIMER_PTV_EN | >> - ((cycles > 1) ? (cycles - 1) : 0), /* n+1 scheme */ >> - reg_base + TIMER_PTV); >> + writel_relaxed(TIMER_PTV_EN | (cycles - 1), reg_base + TIMER_PTV); > > Maybe keep the n+1 scheme comment and explain why we don't need to > handle the case where cycles < 1. That way it becomes crystal clear that > we don't need it, so we decrease the chances of somebody coming around > and trying to "fix" this. Okay, I'll extend the commit message and add a clarifying comment to the code in v2.
