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: NTao Ren <taoren@fb.com> Reviewed-by: NLinus Walleij <linus.walleij@linaro.org> Tested-by: NLei YU <mine260309@gmail.com> Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
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