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Commit 3ef06653 authored by Huacai Chen's avatar Huacai Chen Committed by Ralf Baechle
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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
c6eb3f70 ("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 f9eccf24 ("clocksource/drivers
/vt8500: Increase the minimum delta").

By the way, this patch ensures hpet count/compare to be 32-bit long.

Signed-off-by: default avatarHuacai Chen <chenhc@lemote.com>
Cc: John Crispin <john@phrozen.org>
Cc: Steven J . Hill <Steven.Hill@imgtec.com>
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: stable@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13819/


Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent 07d69579

arch/mips/loongson64/loongson-3/hpet.c

+7 −7
Original line number Diff line number Diff line
@@ -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;