diff options
| author | Tao Ren <taoren@fb.com> | 2018-09-19 15:13:31 -0700 |
|---|---|---|
| committer | Daniel Lezcano <daniel.lezcano@linaro.org> | 2018-09-24 06:13:31 +0200 |
| commit | 4451d3f59f2a6f95e5d205c2d04ea072955d080d (patch) | |
| tree | 7ff03084e4fd99f675497adfbc66fb67ba335ac7 /drivers/clocksource | |
| parent | 3b7d96a0dbb6b630878597a1838fc39f808b761b (diff) | |
| download | lwn-4451d3f59f2a6f95e5d205c2d04ea072955d080d.tar.gz lwn-4451d3f59f2a6f95e5d205c2d04ea072955d080d.zip | |
clocksource/drivers/fttmr010: Fix set_next_event handler
Currently, the aspeed MATCH1 register is updated to <current_count -
cycles> in set_next_event handler, with the assumption that COUNT
register value is preserved when the timer is disabled and it continues
decrementing after the timer is enabled. But the assumption is wrong:
RELOAD register is loaded into COUNT register when the aspeed timer is
enabled, which means the next event may be delayed because timer
interrupt won't be generated until <0xFFFFFFFF - current_count +
cycles>.
The problem can be fixed by updating RELOAD register to <cycles>, and
COUNT register will be re-loaded when the timer is enabled and interrupt
is generated when COUNT register overflows.
The test result on Facebook Backpack-CMM BMC hardware (AST2500) shows
the issue is fixed: without the patch, usleep(100) suspends the process
for several milliseconds (and sometimes even over 40 milliseconds);
after applying the fix, usleep(100) takes averagely 240 microseconds to
return under the same workload level.
Signed-off-by: Tao Ren <taoren@fb.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Lei YU <mine260309@gmail.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Diffstat (limited to 'drivers/clocksource')
| -rw-r--r-- | drivers/clocksource/timer-fttmr010.c | 18 |
1 files changed, 11 insertions, 7 deletions
diff --git a/drivers/clocksource/timer-fttmr010.c b/drivers/clocksource/timer-fttmr010.c index c020038ebfab..cf93f6419b51 100644 --- a/drivers/clocksource/timer-fttmr010.c +++ b/drivers/clocksource/timer-fttmr010.c @@ -130,13 +130,17 @@ static int fttmr010_timer_set_next_event(unsigned long cycles, cr &= ~fttmr010->t1_enable_val; writel(cr, fttmr010->base + TIMER_CR); - /* Setup the match register forward/backward in time */ - cr = readl(fttmr010->base + TIMER1_COUNT); - if (fttmr010->count_down) - cr -= cycles; - else - cr += cycles; - writel(cr, fttmr010->base + TIMER1_MATCH1); + if (fttmr010->count_down) { + /* + * ASPEED Timer Controller will load TIMER1_LOAD register + * into TIMER1_COUNT register when the timer is re-enabled. + */ + writel(cycles, fttmr010->base + TIMER1_LOAD); + } else { + /* Setup the match register forward in time */ + cr = readl(fttmr010->base + TIMER1_COUNT); + writel(cr + cycles, fttmr010->base + TIMER1_MATCH1); + } /* Start */ cr = readl(fttmr010->base + TIMER_CR); |