From 4451d3f59f2a6f95e5d205c2d04ea072955d080d Mon Sep 17 00:00:00 2001 From: Tao Ren Date: Wed, 19 Sep 2018 15:13:31 -0700 Subject: [PATCH] clocksource/drivers/fttmr010: Fix set_next_event handler Currently, the aspeed MATCH1 register is updated to 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 , 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 Reviewed-by: Linus Walleij Tested-by: Lei YU Signed-off-by: Daniel Lezcano --- drivers/clocksource/timer-fttmr010.c | 18 +++++++++++------- 1 file 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);