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The counters in each GIC are not synchronised in any way, so they can drift relative to one another through the lifetime of the system. This is problematic for a clocksource which ought to be global. Avoid problems by always accessing cluster 0's counter, using cross-cluster register access. This adds overhead so we only do so on systems where we actually have CPUs present in multiple clusters. For now, be extra conservative and don't use gic counter for vdso or sched_clock in this case. Signed-off-by: Paul Burton Signed-off-by: Chao-ying Fu Signed-off-by: Dragan Mladjenovic diff --git a/drivers/clocksource/mips-gic-timer.c b/drivers/clocksource/mips-gic-timer.c index be4175f415ba..6632d314a2c0 100644 --- a/drivers/clocksource/mips-gic-timer.c +++ b/drivers/clocksource/mips-gic-timer.c @@ -170,6 +170,37 @@ static u64 gic_hpt_read(struct clocksource *cs) return gic_read_count(); } +static u64 gic_hpt_read_multicluster(struct clocksource *cs) +{ + unsigned int hi, hi2, lo; + u64 count; + + mips_cm_lock_other(0, 0, 0, CM_GCR_Cx_OTHER_BLOCK_GLOBAL); + + if (mips_cm_is64) { + count = read_gic_redir_counter(); + goto out; + } + + hi = read_gic_redir_counter_32h(); + while (true) { + lo = read_gic_redir_counter_32l(); + + /* If hi didn't change then lo didn't wrap & we're done */ + hi2 = read_gic_redir_counter_32h(); + if (hi2 == hi) + break; + + /* Otherwise, repeat with the latest hi value */ + hi = hi2; + } + + count = (((u64)hi) << 32) + lo; +out: + mips_cm_unlock_other(); + return count; +} + static struct clocksource gic_clocksource = { .name = "GIC", .read = gic_hpt_read, @@ -204,6 +235,11 @@ static int __init __gic_clocksource_init(void) /* Calculate a somewhat reasonable rating value. */ gic_clocksource.rating = 200 + gic_frequency / 10000000; + if (mips_cps_multicluster_cpus()) { + gic_clocksource.read = &gic_hpt_read_multicluster; + gic_clocksource.vdso_clock_mode = VDSO_CLOCKMODE_NONE; + } + ret = clocksource_register_hz(&gic_clocksource, gic_frequency); if (ret < 0) pr_warn("Unable to register clocksource\n"); @@ -262,7 +298,8 @@ static int __init gic_clocksource_of_init(struct device_node *node) * stable CPU frequency or on the platforms with CM3 and CPU frequency * change performed by the CPC core clocks divider. */ - if (mips_cm_revision() >= CM_REV_CM3 || !IS_ENABLED(CONFIG_CPU_FREQ)) { + if ((mips_cm_revision() >= CM_REV_CM3 || !IS_ENABLED(CONFIG_CPU_FREQ)) && + !mips_cps_multicluster_cpus()) { sched_clock_register(mips_cm_is64 ? gic_read_count_64 : gic_read_count_2x32, 64, gic_frequency); -- 2.17.1