Messages in this thread | | | Date | Mon, 1 Jul 2013 10:15:51 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCHv2 4/8] clocksource: sun4i: Fix the next event code |
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On Sat, 29 Jun 2013, Maxime Ripard wrote: > On Fri, Jun 28, 2013 at 11:27:25PM +0200, Thomas Gleixner wrote: > > On Fri, 28 Jun 2013, Maxime Ripard wrote: > > > On Fri, Jun 28, 2013 at 10:13:08PM +0200, Thomas Gleixner wrote: > > > > On Fri, 28 Jun 2013, Maxime Ripard wrote: > > > > > @@ -61,9 +62,14 @@ static void sun4i_clkevt_mode(enum clock_event_mode mode, > > > > > static int sun4i_clkevt_next_event(unsigned long evt, > > > > > struct clock_event_device *unused) > > > > > { > > > > > - u32 u = readl(timer_base + TIMER_CTL_REG(0)); > > > > > - writel(evt, timer_base + TIMER_CNTVAL_REG(0)); > > > > > - writel(u | TIMER_CTL_ENABLE | TIMER_CTL_AUTORELOAD, > > > > > + u32 val = readl(timer_base + TIMER_CTL_REG(0)); > > > > > + writel(val & ~TIMER_CTL_ENABLE, timer_base + TIMER_CTL_REG(0)); > > > > > + udelay(1); > > > > > > > > That udelay() is more than suspicious. Is there really no other way to > > > > deal with that hardware? > > > > > > > > If no, you really need to put a proper explanation for that into the code. > > > > > > The datasheet states that you have to wait for two ticks of the timer > > > clock source (in that case, 24MHz, which makes it around 80-85ns) before > > > you can actually enable it back. > > > > > > I didn't came up with a better solution. > > > > 80-85ns is definitely way less than 1us. > > > > Why not reading the counter register and wait for 2 or 3 cycles to > > elapse instead of wasting a full microsecond evertime ? > > Yes, but then we fall back to the discussion we had in the v1 about the > latch needed to read the counter, which would already take more time > than what we have to wait for. > > Maybe we can use the second timer that we use for the clocksource > though: it's always running, already set up, work at the same rate and > we will only read it, so we won't change its monotonic nature.
Right. That will give you exact the information you need and make for the shortest waiting time.
Thanks,
tglx
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