[RFC v6 04/23] clocksource: em_sti: compute rate before registration

Nicolai Stange
2016-09-09T20:03:54Z

With the upcoming NTP correction related rate adjustments to be implemented
in the clockevents core, the latter needs to get informed about every rate
change of a clockevent device made after its registration.

Currently, em_sti violates this requirement in that it registers its
clockevent device with a dummy rate and sets its final rate through
clockevents_config() called from its ->set_state_oneshot().

This patch moves the setting of the clockevent device's rate to its
registration.

I checked all current em_sti users in arch/arm/mach-shmobile and right now,
none of them changes any rate in any clock tree relevant to em_sti after
their respective time_init(). Since all em_sti instances are created after
time_init(), none of them should ever observe any clock rate changes.

- Determine the ->rate value in em_sti_probe() at device probing rather
than at first usage.
- Set the clockevent device's rate at its registration.
- Although not strictly necessary for the upcoming clockevent core changes,
set the clocksource's rate at its registration for consistency.

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
---

Notes:
For a detailed analysis of the current em_sti users, please see
https://nicst.de/ced-clk-rate-change-analysis/em_sti-cgitted.html

Compile-only tested on ARCH=arm.

drivers/clocksource/em_sti.c | 24 ++++++++++++++----------
1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/drivers/clocksource/em_sti.c b/drivers/clocksource/em_sti.c
index 46750c0..6168d18 100644
--- a/drivers/clocksource/em_sti.c
+++ b/drivers/clocksource/em_sti.c
@@ -205,13 +205,9 @@ static cycle_t em_sti_clocksource_read(struct clocksource *cs)

static int em_sti_clocksource_enable(struct clocksource *cs)
{
- int ret;
struct em_sti_priv *p = cs_to_em_sti(cs);

- ret = em_sti_start(p, USER_CLOCKSOURCE);
- if (!ret)
- __clocksource_update_freq_hz(cs, p->rate);
- return ret;
+ return em_sti_start(p, USER_CLOCKSOURCE);
}

static void em_sti_clocksource_disable(struct clocksource *cs)
@@ -240,8 +236,7 @@ static int em_sti_register_clocksource(struct em_sti_priv *p)

dev_info(&p->pdev->dev, "used as clock source\n");

- /* Register with dummy 1 Hz value, gets updated in ->enable() */
- clocksource_register_hz(cs, 1);
+ clocksource_register_hz(cs, p->rate);
return 0;
}

@@ -263,7 +258,6 @@ static int em_sti_clock_event_set_oneshot(struct clock_event_device *ced)

dev_info(&p->pdev->dev, "used for oneshot clock events\n");
em_sti_start(p, USER_CLOCKEVENT);
- clockevents_config(&p->ced, p->rate);
return 0;
}

@@ -294,8 +288,7 @@ static void em_sti_register_clockevent(struct em_sti_priv *p)

dev_info(&p->pdev->dev, "used for clock events\n");

- /* Register with dummy 1 Hz value, gets updated in ->set_state_oneshot() */
- clockevents_config_and_register(ced, 1, 2, 0xffffffff);
+ clockevents_config_and_register(ced, p->rate, 2, 0xffffffff);
}

static int em_sti_probe(struct platform_device *pdev)
@@ -344,11 +337,22 @@ static int em_sti_probe(struct platform_device *pdev)
goto err_clk_put;
}

+ ret = clk_enable(p->clk);
+ if (ret < 0) {
+ dev_err(&p->pdev->dev, "cannot enable clock\n");
+ goto err_clk_unprepare;
+ }
+ p->rate = clk_get_rate(p->clk);
+ clk_disable(p->clk);
+
raw_spin_lock_init(&p->lock);
em_sti_register_clockevent(p);
em_sti_register_clocksource(p);
return 0;

+err_clk_unprepare:
+ clk_unprepare(p->clk);
+
err_clk_put:
clk_put(p->clk);
return ret;
--
2.9.3