From: u.kleine-koenig@pengutronix.de (Uwe Kleine-König)
To: linux-arm-kernel@lists.infradead.org
Subject: Timer on i.MX28 moving backwards
Date: Fri, 7 Sep 2018 09:21:05 +0200 [thread overview]
Message-ID: <20180907072105.m47r3rjf2dd3jlv6@pengutronix.de> (raw)
In-Reply-To: <20180906213925.GU30658@n2100.armlinux.org.uk>
On Thu, Sep 06, 2018 at 10:39:25PM +0100, Russell King - ARM Linux wrote:
> On Thu, Sep 06, 2018 at 10:02:02PM +0200, Uwe Kleine-K?nig wrote:
> > +cycle_t mxs_clocksource_mmio_readl_down(struct clocksource *c)
> > +{
> > + cycle_t ret = ~(cycle_t)readl_relaxed(to_mmio_clksrc(c)->reg) & c->mask;
> > + trace_printk("time = %llx\n", ret);
>
> I think it may be worth re-running your test with:
>
> u32 one, two;
>
> one = readl_relaxed(to_mmio_clksrc(c)->reg);
> two = readl_relaxed(to_mmio_clksrc(c)->reg);
> trace_printk("time=0x%08x:0x%08x\n", one, two);
>
> return ~(cycle_t)two & c->mask;
>
> and compare the values not only between each call but also between
> each read of the register. It could be a synchronisation issue when
> reading the timer register, in which case you may find just one read
> is incorrect.
Good idea, this is a part of a trace I captured with this implemented:
mrp62439d-224 [000] d..h2.. 790.936689: mxs_clocksource_mmio_readl_down: time = 0x948e3d1a:0x948e3d14
mrp62439d-224 [000] ....... 790.936689: mxs_clocksource_mmio_readl_down: time = 0x948e4d26:0x948e4d20
mrp62439d-224 [000] ....... 790.936904: mxs_clocksource_mmio_readl_down: time = 0x948e3690:0x948e368a
hmm, I'm unsure what to think now.
Uwe
--
Pengutronix e.K. | Uwe Kleine-K?nig |
Industrial Linux Solutions | http://www.pengutronix.de/ |
next prev parent reply other threads:[~2018-09-07 7:21 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-06 20:02 Timer on i.MX28 moving backwards Uwe Kleine-König
2018-09-06 21:39 ` Russell King - ARM Linux
2018-09-07 7:21 ` Uwe Kleine-König [this message]
2018-09-07 8:38 ` Uwe Kleine-König
2018-09-07 9:08 ` Russell King - ARM Linux
2018-09-07 10:00 ` Uwe Kleine-König
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