From mboxrd@z Thu Jan 1 00:00:00 1970 From: daniel.lezcano@linaro.org (Daniel Lezcano) Date: Tue, 5 Jan 2016 10:01:07 +0100 Subject: [PATCH v3 1/3] clocksource/vt8500: Increase the minimum delta In-Reply-To: <1451654683-2401-2-git-send-email-v1ron@mail.ru> References: <1451654683-2401-1-git-send-email-v1ron@mail.ru> <1451654683-2401-2-git-send-email-v1ron@mail.ru> Message-ID: <568B8653.2010301@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 01/01/2016 02:24 PM, Roman Volkov wrote: > From: Roman Volkov > > The vt8500 clocksource driver declares itself as capable to handle the > minimum delay of 4 cycles by passing the value into > clockevents_config_and_register(). The vt8500_timer_set_next_event() > requires the passed cycles value to be at least 16. The impact is that > userspace hangs in nanosleep() calls with small delay intervals. > > This problem is reproducible in Linux 4.2 starting from: > c6eb3f70d448 ('hrtimer: Get rid of hrtimer softirq') > > Signed-off-by: Roman Volkov > Acked-by: Alexey Charkov Hi Roman, I looked at the email thread, and IIUC if set_next_event fails, the system freeze. Your patch fixes the issue for your driver but not the real issue because if set_next_event fails, at least a warning should appear in the log or better nanosleep should fail gracefully. BTW why min delta is MIN_OSCR_DELTA * 2 in clockevents_config_and_register ? > --- > drivers/clocksource/vt8500_timer.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/drivers/clocksource/vt8500_timer.c b/drivers/clocksource/vt8500_timer.c > index a92e94b..dfc3bb4 100644 > --- a/drivers/clocksource/vt8500_timer.c > +++ b/drivers/clocksource/vt8500_timer.c > @@ -50,6 +50,8 @@ > > #define msecs_to_loops(t) (loops_per_jiffy / 1000 * HZ * t) > > +#define MIN_OSCR_DELTA 16 > + > static void __iomem *regbase; > > static cycle_t vt8500_timer_read(struct clocksource *cs) > @@ -80,7 +82,7 @@ static int vt8500_timer_set_next_event(unsigned long cycles, > cpu_relax(); > writel((unsigned long)alarm, regbase + TIMER_MATCH_VAL); > > - if ((signed)(alarm - clocksource.read(&clocksource)) <= 16) > + if ((signed)(alarm - clocksource.read(&clocksource)) <= MIN_OSCR_DELTA) > return -ETIME; > > writel(1, regbase + TIMER_IER_VAL); > @@ -151,7 +153,7 @@ static void __init vt8500_timer_init(struct device_node *np) > pr_err("%s: setup_irq failed for %s\n", __func__, > clockevent.name); > clockevents_config_and_register(&clockevent, VT8500_TIMER_HZ, > - 4, 0xf0000000); > + MIN_OSCR_DELTA * 2, 0xf0000000); > } > > CLOCKSOURCE_OF_DECLARE(vt8500, "via,vt8500-timer", vt8500_timer_init); > -- Linaro.org ? Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog