From 3ef06653987d4c4536b408321edf0e5caa2a317f Mon Sep 17 00:00:00 2001 From: Huacai Chen Date: Thu, 21 Jul 2016 14:27:51 +0800 Subject: [PATCH] MIPS: hpet: Increase HPET_MIN_PROG_DELTA and decrease HPET_MIN_CYCLES At first, we prefer to use mips clockevent device, so we decrease the rating of hpet clockevent device. For hpet, if HPET_MIN_PROG_DELTA (minimum delta of hpet programming) is too small and HPET_MIN_CYCLES (threshold of -ETIME checking) is too large, then hpet_next_event() can easily return -ETIME. After commit c6eb3f70d44828 ("hrtimer: Get rid of hrtimer softirq") this will cause a RCU stall. So, HPET_MIN_PROG_DELTA must be sufficient that we don't re-trip the -ETIME check -- if we do, we will return -ETIME, forward the next event time, try to set it, return -ETIME again, and basically lock the system up. Meanwhile, HPET_MIN_CYCLES doesn't need to be too large, 16 cycles is enough. This solution is similar to commit f9eccf24615672 ("clocksource/drivers /vt8500: Increase the minimum delta"). By the way, this patch ensures hpet count/compare to be 32-bit long. Signed-off-by: Huacai Chen Cc: John Crispin Cc: Steven J . Hill Cc: Fuxin Zhang Cc: Zhangjin Wu Cc: linux-mips@linux-mips.org Cc: stable@vger.kernel.org Patchwork: https://patchwork.linux-mips.org/patch/13819/ Signed-off-by: Ralf Baechle --- arch/mips/loongson64/loongson-3/hpet.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/arch/mips/loongson64/loongson-3/hpet.c b/arch/mips/loongson64/loongson-3/hpet.c index 249039af66c4..4788bea62a6a 100644 --- a/arch/mips/loongson64/loongson-3/hpet.c +++ b/arch/mips/loongson64/loongson-3/hpet.c @@ -13,8 +13,8 @@ #define SMBUS_PCI_REG64 0x64 #define SMBUS_PCI_REGB4 0xb4 -#define HPET_MIN_CYCLES 64 -#define HPET_MIN_PROG_DELTA (HPET_MIN_CYCLES + (HPET_MIN_CYCLES >> 1)) +#define HPET_MIN_CYCLES 16 +#define HPET_MIN_PROG_DELTA (HPET_MIN_CYCLES * 12) static DEFINE_SPINLOCK(hpet_lock); DEFINE_PER_CPU(struct clock_event_device, hpet_clockevent_device); @@ -157,14 +157,14 @@ static int hpet_tick_resume(struct clock_event_device *evt) static int hpet_next_event(unsigned long delta, struct clock_event_device *evt) { - unsigned int cnt; - int res; + u32 cnt; + s32 res; cnt = hpet_read(HPET_COUNTER); - cnt += delta; + cnt += (u32) delta; hpet_write(HPET_T0_CMP, cnt); - res = (int)(cnt - hpet_read(HPET_COUNTER)); + res = (s32)(cnt - hpet_read(HPET_COUNTER)); return res < HPET_MIN_CYCLES ? -ETIME : 0; } @@ -230,7 +230,7 @@ void __init setup_hpet_timer(void) cd = &per_cpu(hpet_clockevent_device, cpu); cd->name = "hpet"; - cd->rating = 320; + cd->rating = 100; cd->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT; cd->set_state_shutdown = hpet_set_state_shutdown; cd->set_state_periodic = hpet_set_state_periodic; -- 2.20.1