[PATCH v4 09/10] clocksource/drivers/tegra: Lower clocksource rating for some Tegra's

Dmitry Osipenko
2019-06-03T19:04:30Z

Arch-timer is more preferable for a range of Tegra SoC generations as
it has higher precision and is not affect by any kind of problems.

Pointed-out-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
drivers/clocksource/timer-tegra20.c | 30 +++++++++++++++++++++++++----
1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/clocksource/timer-tegra20.c b/drivers/clocksource/timer-tegra20.c
index 1a3ee928e9a5..9406855781ff 100644
--- a/drivers/clocksource/timer-tegra20.c
+++ b/drivers/clocksource/timer-tegra20.c
@@ -107,7 +107,6 @@ static DEFINE_PER_CPU(struct timer_of, tegra_to) = {

.clkevt = {
.name = "tegra_timer",
- .rating = 460,
.features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_PERIODIC,
.set_next_event = tegra_timer_set_next_event,
.set_state_shutdown = tegra_timer_shutdown,
@@ -217,7 +216,8 @@ static inline unsigned int tegra_irq_idx_for_cpu(int cpu, bool tegra20)
return TIMER10_IRQ_IDX + cpu;
}

-static int __init tegra_init_timer(struct device_node *np, bool tegra20)
+static int __init tegra_init_timer(struct device_node *np, bool tegra20,
+ int rating)
{
struct timer_of *to;
int cpu, ret;
@@ -280,6 +280,7 @@ static int __init tegra_init_timer(struct device_node *np, bool tegra20)

cpu_to = per_cpu_ptr(&tegra_to, cpu);
cpu_to->of_base.base = timer_reg_base + base;
+ cpu_to->clkevt.rating = rating;
cpu_to->clkevt.cpumask = cpumask_of(cpu);
cpu_to->clkevt.irq = irq_of_parse_and_map(np, idx);
if (!cpu_to->clkevt.irq) {
@@ -339,13 +340,34 @@ static int __init tegra_init_timer(struct device_node *np, bool tegra20)

static int __init tegra210_init_timer(struct device_node *np)
{
- return tegra_init_timer(np, false);
+ /*
+ * Arch-timer can't survive across power cycle of CPU core and
+ * after CPUPORESET signal due to a system design shortcoming,
+ * hence tegra-timer is more preferable on Tegra210.
+ */
+ return tegra_init_timer(np, false, 460);
}
TIMER_OF_DECLARE(tegra210_timer, "nvidia,tegra210-timer", tegra210_init_timer);

static int __init tegra20_init_timer(struct device_node *np)
{
- return tegra_init_timer(np, true);
+ int rating;
+
+ /*
+ * Tegra20 and Tegra30 have Cortex A9 CPU that has a TWD timer,
+ * that timer runs off the CPU clock and hence is subjected to
+ * a jitter caused by DVFS clock rate changes. Tegra-timer is
+ * more preferable for older Tegra's, while later SoC generations
+ * have arch-timer as a main per-CPU timer and it is not affected
+ * by DVFS changes.
+ */
+ if (of_machine_is_compatible("nvidia,tegra20") ||
+ of_machine_is_compatible("nvidia,tegra30"))
+ rating = 460;
+ else
+ rating = 330;
+
+ return tegra_init_timer(np, true, rating);
}
TIMER_OF_DECLARE(tegra20_timer, "nvidia,tegra20-timer", tegra20_init_timer);

--
2.21.0