linux-kernel - [RFC v4 04/22] clocksource: em_sti: compute rate before registration

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Message-Id: <20160822233320.4548-5-nicstange@gmail.com>
Date:   Tue, 23 Aug 2016 01:33:02 +0200
From:   Nicolai Stange <nicstange@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     John Stultz <john.stultz@...aro.org>, linux-kernel@...r.kernel.org,
        Nicolai Stange <nicstange@...il.com>
Subject: [RFC v4 04/22] clocksource: em_sti: compute rate before registration

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@...il.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;
-- 
2.9.2