1 // SPDX-License-Identifier: GPL-2.0+
4 * David Feng <fenghua@phytium.com.cn>
9 #include <asm/system.h>
11 DECLARE_GLOBAL_DATA_PTR;
14 * Generic timer implementation of get_tbclk()
16 unsigned long get_tbclk(void)
19 asm volatile("mrs %0, cntfrq_el0" : "=r" (cntfrq));
23 #ifdef CONFIG_SYS_FSL_ERRATUM_A008585
25 * FSL erratum A-008585 says that the ARM generic timer counter "has the
26 * potential to contain an erroneous value for a small number of core
27 * clock cycles every time the timer value changes".
28 * This sometimes leads to a consecutive counter read returning a lower
29 * value than the previous one, thus reporting the time to go backwards.
30 * The workaround is to read the counter twice and only return when the value
31 * was the same in both reads.
32 * Assumes that the CPU runs in much higher frequency than the timer.
34 unsigned long timer_read_counter(void)
40 asm volatile("mrs %0, cntpct_el0" : "=r" (cntpct));
41 asm volatile("mrs %0, cntpct_el0" : "=r" (temp));
42 while (temp != cntpct) {
43 asm volatile("mrs %0, cntpct_el0" : "=r" (cntpct));
44 asm volatile("mrs %0, cntpct_el0" : "=r" (temp));
49 #elif CONFIG_SUNXI_A64_TIMER_ERRATUM
51 * This erratum sometimes flips the lower 11 bits of the counter value
52 * to all 0's or all 1's, leading to jumps forwards or backwards.
53 * Backwards jumps might be interpreted all roll-overs and be treated as
55 * The workaround is to check whether the lower 11 bits of the counter are
56 * all 0 or all 1, then discard this value and read again.
57 * This occasionally discards valid values, but will catch all erroneous
58 * reads and fixes the problem reliably. Also this mostly requires only a
59 * single read, so does not have any significant overhead.
60 * The algorithm was conceived by Samuel Holland.
62 unsigned long timer_read_counter(void)
68 asm volatile("mrs %0, cntpct_el0" : "=r" (cntpct));
69 } while (((cntpct + 1) & GENMASK(10, 0)) <= 1);
75 * timer_read_counter() using the Arm Generic Timer (aka arch timer).
77 unsigned long timer_read_counter(void)
82 asm volatile("mrs %0, cntpct_el0" : "=r" (cntpct));
88 uint64_t get_ticks(void)
90 unsigned long ticks = timer_read_counter();
97 unsigned long usec2ticks(unsigned long usec)
101 ticks = ((usec * (get_tbclk()/1000)) + 500) / 1000;
103 ticks = ((usec / 10) * (get_tbclk() / 100000));
108 ulong timer_get_boot_us(void)
110 u64 val = get_ticks() * 1000000;
112 return val / get_tbclk();